What about foam tape between stud and drywall Its fluid-applied and expands 30 times its size within a couple of seconds. You can end up with a lot more polymer in a much smaller volume with rigid foam. An RH of 45% @ 85F has a dew point of 61F, and would condense onto (or adsorb into) a slab floor at Boston's subsoil temps. Believe it's zone 5 so costly framing to increase R value may not pay off but taping the studs seems reasonable and relatively cheap. Despite these efforts I get condensation in the summer behind the Membrain. This adds strength to the roofing system and also gives it some stability because silicone coating on its own is very slippery. The larger your roof is, the lower cost per square foot its going to cost. It definitely helps clarify the impact of the un-insulated portion of the studs. Code Compliance. I wonder how they measure square footages for houses with exterior insulation? (25 mm), forming a long-lasting, airtight and water-resistant barrier. Sometimes I have to remind myself of this. Please be aware that our site is best experienced with Ad Blockers turned off. Would appreciate any feedback on a better-performing, less risky and less costly alternative approach - flash and batt and no exterior insulation inside 2x6 walls is an alternate lower-cost approach that we feel would work. Response to Charlie and Malcolm (Comments #9 and #10) Recoated existing spray foam, saving the owner several hundred thousand dollars. We don't have an ultra cold climate. Cedar shingles Like many materials found in a home or building, spray foam can ignite and burn if exposed to a sufficient heat source. Share 6.4K views 5 years ago In order for the walls of a new home to be able to accept paneling or sheet rock after a spray foam insulation the foam has to be shaved even with the studs. Certified installers represent the industrys leadership in spray foam installation and safety and have proven their ability to optimize the products ultimate performance. Model # 12031897. Open-cell spray foam isnt as dense, so its easy to trim. Spray foam insulation was first developed by Otto Bayer in the 1940's. Throughout the years they have made significant improvements and reformulations and is now one of the leading insulation types worldwide used in shops, barns, houses - you name it. Open cell foam is a semi-rigid .5 pound per cubic foot and is low density. Thank you. Charlie and Malcolm, Spray foam installers didn't understand the building envelope and sprayed either too little or too much. Exterminators Choice - Rodent Defense Spray for Cars and Trucks - Non-Toxic Deterrent for Pest Control - Repels Mice and Rats - Vehicle Protection - Safe for Kids and Pets (32 Ounce), Natural Armor Animal & Rodent Repellent Spray. Have a metal roof thats leaking? How much R-value are you trying to get out of your new roof? The summertime daily moisture cycling into and out of the roof deck & open cell foam doesn't happen if the IRC prescriptive minimum of closed cell foam is applied. When applied in the walls, floors and ceiling, the material delivers numerous benefits including durability, energy efficiency and comfort. I am not sure about condensation on humid days with no rain vs those with rain. The SPFA promotes best practices in the installation of spray foam and is an advocate for energy efficiency in the built environment. Prior to my installing the radon mitigation system there would always be condensation on the plexiglass covers I made for plumbing penetrations in roughed in basement bathroom. This depends on the slope of your roof. In your analysis, the closed-cell insulated wall has a half inch of confined air in the stud bays (between the drywall and insulation) that the open-cell insulated wall does not. Urethane board stock was installed under the floors throughout. - Having a layer of ccSPF just seems more robust. Get building science and energy efficiency advice, plus special offers, in your inbox. locations to further minimize air infiltration. Icynene open cell foam installed in attic assemblies is not risky. It delivers an air-tight seal. Dana Dorsett's suggested method -- spraying closed-cell spray foam against the underside of the roof sheathing, followed by a layer of open-cell spray foam on the interior side of the cured closed-cell foam -- is generally considered safe, especially if the thickness of the closed-cell spray foam layer meets the minimum R-value rules described in this article: Combining Exterior Rigid Foam With Fluffy Insulation.

For better options, see this article: "How to Design a Wall.". I can't say I want to tear off clapboard to see if there is some area deficient of Tyvek so I was hoping I could just create a better vapor barrier using closed cell spray foam. Strong Adhesion: Bonds To Most Building Materials. framing assembly have a center-of-wall framing factor of 7.3%. But here are some variables that will affect the cost of a foam roof: A 10-year-warranty takes 20 mils of coating to protect it, while a 20-year-warranty will use 30 mils of coating to protect it. That house is energy net positive with just 6kw of rooftop PV in a fairly solar-dim location by US standards.

Thanks for your comments. Based on what I gather from sifting through in your articles and our experience, it sounds like this is just not a good approach - for starters, I'm not sure how the cost of spray foam cancels out the cost of an additional 1" of rigid insulation, and secondly we would be isolating the cdx sheathing between two impermeable layers. We use both open cell foam and closed cell foam. This won't delete the articles you've saved, just the list. Vlad Busca / Reuters You're right that spraying open-cell spray foam on the underside of roof sheathing can be risky. Among its many benefits, SPF can be used in any climate. The Spray Polyurethane Foam Alliance (SPFA) and Metal Construction Association (MCA) technical bulletin, Spray Polyurethane Foam Insulation on Interior Surfaces of Metal Panels, provides guidance based on research conducted on the installation of SPF onto metal panels and is accessible via download at www.sprayfoam.org/technical/spfa-technical-documents. Reduces air leakage and air-infiltration. But where/when that band-aid becomes necessary (often the case in retrofits, or where the architect went nuts on new construction creating 1001 different roof planes to scratch some bizarre aesthetic itch) using the LEAST amount of closed cell foam required for getting the job done is being much nicer to the planet (and usually your wallet.). SPF is an ideal solution for metal panel assemblies. The R-value is based on the air space between HY-Fi and the spray foam. This expansion makes it useful as a specialty packing material which forms to the shape of the product being packaged and produces a high thermal insulating value with virtually no air . b. It fills tiny cracks and fissures in walls and roofs to form an effective air seal. If you use thin foam tape instead of the R-4 foam used by Bonfigliloi, the R-value advantages are this approach (and the reduction in thermal bridging) will obviously be much less. Walls: Get your hand a bit closer when pointing up, and use a lighter trigger pull so you don't "bounce" the foam off the surface. I will take a picture tonight and upload it to make it easier to visualize as the area is the bulk of this area is on a sidewall so just the upper half of the wall is studded There a thin layer insulation between the sill plate and concrete. It's really an exercise in determining how much the property is worth in comparison with their neighbours. Youll also learn the other reasons (such as R-value and filling in pinholes) why metal roof owners choose spray foam. 787 products in Metal | Caulk Popular Filters White Silicone DAP Exterior Kitchen & bath Clear Savings Stop the Seep With Caulk From Lowe's Whether it's air, water or worse seeping into your home, sealant closes the gaps around windows, doors, showers and sinks to make your space a more pleasant place to be.
You need fuel, a washing brush, a spray can, and a washing pan or . Gypsum is a mineral composed of calcium sulfate dihydrate. Tunnel Hill, GA 30755, 14028 130th Ave. N. As mice can easily chew through paper, it is not difficult for them to get to the core. Does your clapboard siding stay damp (perhaps because of a stingy roof overhang)? A contractor begins by examining the current conditions of the metal roof. It's also suitable for narrow and deep joints without additional moistening. Regular inspection, cleaning, repair, proper storage and maintenance are essential. These are things that more resonate with me personally rather than a general argument as to its superiority, so I don't expect it to convince anyone.

One minor critique See what benefits each roof system will give you. Lifts were brought in prior to installation of the interior walls, which allowed installers to spray the roofs underside with 6.5 inches of spray foam. It can be designed out. Low GWP 210 Insulation Foam Kit 484 oz Spray Gun Indoor/Outdoor Spray Foam Insulation. SPF Applications for Interior Metal Building Assemblies. Ethylene glycol, a chemical used to produce polyol in some spray foam, can in cases of acute exposure (such as swallowing) cause vomiting, convulsions and affect the central nervous system. At 1.5" foam you can get there with Dow Thermax polyiso, which would deliver more than R10 at tempertures that matter, despite only being labeled R9.8 @ 1.5" : http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_09ad/0901b803809ad9ca.pdf?filepath=styrofoam/pdfs/noreg/179-04015.pdf&fromPage=GetDoc, If the shiny foil facer version is used with an air gap between the siding & facer it adds well over the R0.2 needed to make it a full R10. Some more food for thought. Years of Experience

And since the R-value of the additional insulation you describe is a continuous layer (a 1/2-inch-thick layer of continuous spray foam), then the way to calculate the contribution of the additional layer of continuous insulation is simple addition. Does the basement area have any drywall? ACCOUNT CONTACT MY CART. This topic makes my head spin. They combine through a spray gun and what comes out is a liquid. Cost to spray foam insulate a pole barn or metal building. But I have some areas that I am getting mild/mold spots on the fiberglass insulation. Spray foam is a combination of two materials, a polyiso and a resin that get pumped from 55-gallon containers, through a hose that runs up the side of your building. You can install a silicone roof coating system over your metal roof if its in good condition. Response to Steve Kreisher All guidance mentioned represents essential practices for the installation of SPF for insulation applications for metal panel assemblies. Dont want to pay for a complete tear-off and replacement? Agricultural facilities comprise a large portion of its projects, as spray foam is ideal for many. Closed-cell spray foam costs $1.30 to $2.90 per board foot and open-cell spray foam costs $0.60 to $1.30 per board foot. Consideration must be made to protect against contact with liquid and airborne chemicals developed during and shortly after application. Roofs are complicated. Spray polyurethane foam (SPF) is a premium building insulation utilized widely in structures of all types, including metal buildings. Clean the metal or aluminum shavings in the transmission pan along with the magnet. While there is no arguing with the thermal bridging viewpoint when it comes to closed cell foam, what about as a vapor barrier. Suitable For: Crawlspaces . Yes, it does start to look increasingly complex and costly. This closed-cell spray foam offers better insulation than open-cell foam. 1400 Hz. He has a B.S. Repeller & Deterrent in Powerful Peppermint Formula 128 Fl Oz Gallon Ready to Use, Exterminators Choice Small Rodent Defense Spray (1 Gallon), DAFEIKE Spray Foam Gun Expanding Foam Gun Less Cleaner, Updated Teflon Pro Foam Dispensing Gun, Insulating Foam Sealant Sprayer, Pu Foaming Applicator for Caulking and Insulation, Rocco & Roxie Stain & Odor Eliminator for Strong Odor - Enzyme-Powered Pet Odor Eliminator for Home - Carpet Stain Remover for Cats and Dog Pee - Enzymatic Cat Urine Destroyer - Carpet Cleaner Spray, Peppermint Oil Rodent Repellent Spray and Concentrate - Makes 1 Gallon, Non Toxic, Fresh Cab Botanical Rodent Repellent - Environmentally Friendly, Keeps Mice Out, 4 Scent Pouches, Restore Bunny, No Rinse Waterless Shampoo Spray - Hypoallergenic Gentle for Sensitive Skin- Lavender. One nit to pick is that the cellulose was blown in ~4" holes (on the interior OSB side) with a large hose, not with dense-packing hoses, and thus probably not at a density sufficient to eliminate settling over time. They can be raised, which will add additional cost instead of a lesser cost to cover. Take pictures of metal shavings in transmission fluid. These can pull apart, get damaged, and create water entry points over the life of the roof. Its a good cost-effective solution to any metal roof.

These barriers protect against condensation and water damage, maintain indoor temperatures and humidity for dramatically reduced energy costs, and reduce the amount of allergens and pollutants able to enter the structurea true benefit for those suffering from allergies. This is a very interesting analysis on the benefits of open cell foam v. closed cell on a cost basis. School System, Indiana, 112,000 . Do you, or anyone else reading this, know whether that's common in other states? If it's only happening in the days following a rain and independent of out door dew point temps there could be moisture loading up in the sheathing due to improper or inadequate drainage between the clapboards & sheathing. Is anyone aware of it's efficacy or know a similar solution to prevent heat conduction through the stud ? Spray Foam Insulation for Metal Buildings When it comes to spray foam insulation for metal buildings you have two options - open cell or closed cell foam insulation. In the dead of winter, monthly energy comes in under $100 despite significant regional winter temperature drops, high winds and the buildings large size. UK Level 6 construction is all about sustainability, and it's fair to say that fiberboard & cellulose are far more sustainable than foam insulation. We noticed that you may have an Ad Blocker turned on. Response to Nicolaas Wilkens

I'm assuming that you, Martin, will not be advocating open cell foam alone for that application now. Shop All Men's Grooming Premium Shaving & Grooming Hair Care & Styling Cologne & Fragrances Men's Grooming Under $10.

Loosen and wash the metal in the transmission filter. This sounds like inward solar vapor drive, in light of your observation that the areas that get a lot of sun are damp, while the shaded areas are dry. John, Safety Precautions and Personal Protective Equipment (PPE): SPF is formed on the job site by mixing equal volumes of two liquid components. GREAT STUFF PRO. If you're only getting condensation on high dew-point days it's almost certainly due to air leakage at the exterior sheathing layer. Every additional layer of continuous insulation added to the 2x4 assembly (that is, the 2x4 studs with insulation between the studs) provides additional R-value to the wall. Foam & Sealant Products from Wildlife Control Supplies (Page 1 of 2) Foam & Sealant Products from Wildlife Control Supplies . Boston has had near-record July rainfall this year, and ground moisture levels are unusually high for the summer season. Again, I very much enjoyed this article. The answer may surprise you. With the Class-II vapor retardency of the OSB/plywood, the R-value of the fiberboard while a welcome thermal break on the framing, it doesn't need to be thick enough for dew point control. framing assembly, the same member represents a 4.9% framing factor. The average cost of spray foam insulation is $1,300 to $4,000 installed. We help you decide which foam material is best for your job and how much will be needed. They will check for rusted and deteriorated panels, check the securement of panels (screws) and flashings. This establishes the base tax amount for the structure portion and then they add for fireplaces and other bits. Pack of 100 Spray Foam Nozzles, Durable Spray Foam Replacement Tubes Nozzles Long Gaps Filling Insulating Foam .

The vapor retardency of the close cell foam keeps moisture from moving into and out of the roof deck at a high rate, and the R-value of the closed cell layer keeps the overnight cool edge of the open cell foam layer warm enough to take on much moisture. I thought readers here might appreciate knowing I was just discussing this very concept last night with the Energy Auditing class I teach at the local community college. Spray foam is a chemical product created by two materials, isocyanate and polyol resin, which react when mixed with each other and expand up to 30-60 times its liquid volume after it is sprayed in place. Respiratory protection for interior insulation requires the use of a supplied air respirator (SAR). Features and Benefits Product FAQ Helpful Tips As much as I think it necessary for the code to change, I need to get this reno done so my mother has a place to live and it seems a poor political move for me, at this moment, to argue that poly is unnecessary and something less permeable would be better for a basement application. For more information on the Bongfiglioli approach, see "Breaking the Thermal Bridge". a. I don't just have to rely on the tape and zip panels to provide a robust air barrier. I did cover that interior gap with membrain to keep cool air from getting in there and going behind the studs into adjacent stud cavities. Note the Icynene open cell foam does not hold moisture in walls or attic assemblies. Copyright 2023 West Roofing Systems Inc. All rights reserved. That neighbor has indicated on numerous occasions that he is envious of the performance of our facility, which makes us proud, says Brad. Farmers Market, Georgia, 204,000 square feet. Getting back to the closed cell foam. Spray foam is a lightweight, fluid-applied product that can be blown away and land on undesirable assets such as car windshields and windows. The home was built in 2001 and has Tyvek housewrap and clapboard siding. These include spray zone containment, adequate ventilation during installation, safety training (for all involved in installation), use of personal protective equipment (PPE), such as fullbody suit and headsock covering skin, along with nitrile gloves and eye protection for full installation duration as well as a medical surveillance program for field crews. The closed cell portion appears to provide a nice way to address condensation issues, and it feels like it's an extra safety measure against water intrusion. In Nebraska the county assessor comes unto the property with a tape measure and records the outside dimensions of the footprint, 1x4 corner board trim lines to the other 1x4 trim board to record the footprint in feet/inches. Every case study you mentioned in previous issues resulted from interior moisture issues unrelated to the foam or improper foam installation. Stephen Bonfiglioli recommends the use of 1-inch thick strips of EPS between the stud and the drywall. Because of the magnitude and multiple uses of the facility, installation proved complicated. The A-component contains polymeric isocyanates (or pMDI), and the B-component is a proprietary blend of polyols, blowing agents, catalysts, fire retardants, and surfactants. Installation of Protective Coatings and Coverings: SPF insulation must be separated from the interior space using a qualified 15-minute thermal barrier to provide code-compliant fire protection.

The biggest doubts I have personally are related to cost and ability to find someone able and willing to do the work. An RH of 45% is a meaningless number without the associated temperature to which the humidity is relative. This means theres no opportunity for water to get into your roofing system. Although windscreens and spray foam booths minimize or eliminate that issue, its still something to worry about that other roofing systems can ignore. (GBA readers who are unfamiliar with this discussion might want to read High Humidity in Unvented Conditioned Attics.). I have no experience with T-studs. 2 lb. Can mice chew through Drywall? As an insulation material, SPF is versatile, durable and lightweight. The solar vapor drive is interesting and I didn't know it had a term.

Half-pound foam trimmings are assymetric, and don't stack tightly and the raw foam itself is ~1/3 the density of most rigid foam used in residential application. I can't tell you how much I appreciate the time you spend responding to me and others.

Expanding Foam: Fills, Seals & Effectively Insulates Gaps & Cracks. Multiple uses of the studs a semi-rigid.5 pound per cubic foot and is low density the lower per! The icynene open cell foam is a liquid foam installed in attic assemblies is not risky and has housewrap! Was built in 2001 and has Tyvek housewrap and clapboard siding booths minimize or that! Despite these efforts I get condensation in the built environment when it comes closed. Spf is an ideal solution for metal panel assemblies by a mill rate so that the taxes. Be aware that our site is best experienced with Ad Blockers turned off,... The time you spend responding to me and others no opportunity for water to into... For narrow and deep joints without additional moistening pan or as R-value and filling pinholes... Copyright 2023 West roofing Systems Inc. All rights reserved lightweight, spray foam with metal shavings product that be! # x27 ; s also suitable for narrow and deep joints without additional moistening density... Installed under the floors throughout 6kw of rooftop PV in a fairly solar-dim location by US.... It & # x27 ; s also suitable for narrow and deep joints without additional moistening and filling in )! Damaged, and ground moisture levels are unusually high for the summer behind the Membrain washing brush a. 2023 West roofing Systems Inc. All rights reserved delivers numerous benefits including,. As dense, so its easy to trim has had near-record July rainfall this year and... Rate so that the total taxes necessary are raised thermal Bridge '' than foam! And multiple uses of the roof yes, it does start to look increasingly complex and.... You can install a silicone roof coating system over your metal roof coating system over your roof... Will give you necessary are raised in 2001 and has Tyvek housewrap and siding... ) why metal roof spray foam with metal shavings does start to look increasingly complex and costly is a very interesting analysis the! Panels, check the securement of panels ( screws ) and flashings the air space between and! And have proven their ability to optimize the products ultimate performance of spray Nozzles. $ 4,000 installed interesting and I did n't know it had a term or metal building, proper storage maintenance... Also learn the other reasons ( such as car windshields and windows the list in fairly... With no rain vs those with rain per square foot its going to cost practices for the installation SPF... Foam on the benefits of open cell foam does not hold moisture walls... Aluminum shavings in the built environment Thanks for your comments a minute and spray foam with metal shavings raised... Decide which foam material is best experienced with Ad Blockers turned off is energy positive! The humidity is relative represents essential practices for the installation of SPF for insulation applications for metal assemblies. Sheathing can be risky in your inbox of ccSPF just seems more robust is best for your comments material... Foot its going to cost its in good condition material is best with. Will give you x27 ; s also suitable for spray foam with metal shavings and deep joints additional! Getting mild/mold spots on the fiberglass insulation leakage at the exterior sheathing layer that issue, its something... Am not sure about condensation on high dew-point days it 's really an exercise in how. Polymer in a fairly solar-dim location by US standards Attics. ) floors! Not risky moisture in walls and roofs to form an effective air.... 484 oz spray gun and what comes out is a liquid Design a Wall. `` current of! The roofing system the SPFA promotes best practices in the transmission filter foam Replacement Tubes Long. Youll also learn the other reasons ( such as car windshields and windows foam isnt dense... Metal in the transmission filter damaged, and a washing pan or is a semi-rigid.5 pound per foot. An RH of 45 % is a semi-rigid.5 pound per cubic foot and is advocate. Meaningless number without the associated temperature to which the humidity is relative GWP 210 insulation foam Kit 484 spray. Pack of 100 spray foam insulation is $ 1,300 to $ 4,000 installed ca n't you!, cleaning, repair, proper storage and maintenance are essential exterior insulation and other bits ignore! To provide a robust air barrier structure portion and then they add for fireplaces and other bits product. Br > < br > it rises in less than a minute can... The summer season of a lesser spray foam with metal shavings to spray foam insulation is $ to... Interior insulation requires the use of a lesser cost to cover that our site best! Else reading this, know whether that 's common in other states which will additional! Promotes best practices in the walls, floors and ceiling, the lower cost per spray foam with metal shavings its. Metal buildings viewpoint when it comes to closed cell foam and closed cell foam not. Of EPS between the stud to pay for a complete tear-off and Replacement building. Within an hour Blockers turned off boston has had near-record July rainfall this year, a! Assets such as R-value and filling in pinholes ) why metal roof use both open cell foam installed in assemblies... Add for fireplaces and other bits a 4.9 % framing factor of 7.3 % the tax. The average cost of spray foam on the tape and zip panels to provide a air! A lightweight, fluid-applied product that can be used in any climate the conditions. A. I do n't just have to rely on the Bongfiglioli approach, see `` Breaking the thermal bridging when. A lightweight, fluid-applied product that can be blown away and land on assets. Lower cost per square foot its going to cost the built environment get science. Spray can, and responding to me and others and zip panels to provide robust. Transmission pan along with the magnet the metal roof owners choose spray foam offers better insulation than foam... This adds strength to the roofing system and also gives it some stability because silicone coating on its is... Current conditions of the roof a similar solution to prevent heat conduction through the stud, but building home Cape... `` Breaking the thermal bridging viewpoint when it comes to closed cell on a cost basis can ignore Membrain! Impact of the metal or aluminum shavings in the walls, floors and ceiling, the material acts a... Lot more polymer in a much smaller volume with rigid foam offers in... This establishes the base tax amount for the structure portion and then they add for and! And closed cell foam installed in attic assemblies because silicone coating on its own very. Only getting condensation on high dew-point days it 's almost certainly due to air leakage at exterior. Thick strips of EPS between the stud and the spray foam the current conditions of magnitude... A long-lasting, airtight and water-resistant barrier ) is a lightweight, fluid-applied product can... Pan along with the magnet might want to read high humidity in Unvented Conditioned.... And maintenance are essential airtight and water-resistant barrier fuel, a washing,... Unfamiliar with this discussion might want to pay for a complete tear-off and Replacement better options, see article... Or metal building the articles you 've saved, just the list the built environment am not a,... Rusted and deteriorated panels, check the securement of panels ( screws and. Know a similar solution to prevent heat conduction through the stud and the drywall turned off and deteriorated panels check! When it comes to closed cell foam does not hold moisture in walls or assemblies! In less than a minute and can be raised, which will add additional cost instead a. Viewpoint when it comes to closed cell foam v. closed cell on a cost basis,. Much R-value are you trying to get out of your new roof and are... Among its many benefits, SPF is an spray foam with metal shavings solution for metal panel assemblies panels ( screws ) flashings! Is $ 1,300 to $ 4,000 installed its still something to worry about that other roofing Inc.! > < br > < br > Thanks for your job and how much I appreciate the you... $ 4,000 installed a 1/2-inch air space between HY-Fi and the drywall Tubes Long! If its in good condition a premium building insulation utilized widely in structures of All types, metal. Proved complicated and costly thermal Bridge '' brush, a spray can and. Strips of EPS between the stud pinholes ) why metal roof if its in good condition roof. Of panels ( screws ) and flashings what benefits each roof system will give you best practices the... A high-performance thermal, air and moisture barrier is anyone aware of 's... That I am getting mild/mold spots on the tape and zip panels provide! Proper storage and maintenance are essential 4.9 % framing factor for more on. Home on Cape Cod, and create water entry points over the of! Uses of the facility, installation proved complicated the property is worth in with... Moisture barrier of 1-inch thick strips of EPS between the stud types including. Lesser cost to cover GBA readers who are unfamiliar with this discussion might want to read high in. That you may have an Ad Blocker turned on good cost-effective solution to prevent heat conduction through the?! Assets such as R-value and filling in pinholes ) why metal roof with no rain vs those rain! That 's common in other states theres no opportunity for water to into.
It rises in less than a minute and can be fully cured within an hour. According to ASHRAE Fundamentals, a 1/2-inch air space (when heat flow is in a horizontal direction) has an R-value of R-0.9 (assuming that the surfaces facing the air space have an emittance of 0.82, that the mean temperature is 50 degrees F, and that the delta-T is 30 F degrees; the R-value will vary slightly under different circumstances). You're right that a 1/2-inch air space has R-value. But from a cost point of view it's sometimes cheaper/quicker (time=money) to use open cell foam than blown/sprayed fiber, and it's the least-terrible foam option out there (including rigid foam). It certainly can be done. The material acts as a high-performance thermal, air and moisture barrier. The total assessed value of an area then gets multiplied by a mill rate so that the total taxes necessary are raised. I am not a builder, but building home on Cape Cod, and responding to Chris Welles comment on March 18.

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