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Sill gasket for airtight drywall approach?

Brian Mahoney | Posted in Green Building Techniques on

I am building a double stud wall house in Canada and have just finished the dense pack cellulose behind netting and preparing for ADA. I would like to use a gasket at all necessary areas (top/bottom plate, windows, doors, etc) behind the drywall instead of acoustical sealant to least interrupt the drywall installation i.e. we would put up all necessary gaskets ourselves and then the drywallers would just install as usual. Probably have them add screws every 8 inches to ensure full compression of the gasket and sealing of the joint.

So, I have looked at the price of 3/8″ x 3/16″ closed-cell, self-adhesive neoprene foam strips for sealing drywall to framing and it is going to be very expensive. What do people think of just ripping some regular sill gasket material and stapling it in place as an alternative? Much cheaper.

As well, I have just read another post and realized I could have side stapled the netting to help with the slight bulge. Do people think there will be a problem installing the drywall? Should I use 5/8″ drywall instead? I did not install drywall before the cellulose so the inspector could see the cellulose.


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  1. Riversong | | #1


    It's a bit late to consider ADA gasketing. This has to occur at the framing stage, air-sealing each framing section to the one below it. Then the sealed drywall can become the "membrane" which connects the sealed bottom plate to the sealed top plate.

    Most air leakage in a wood-framed building is at the framing connections: sill to foundation, floor assembly to sill, subfloor to floor framing, bottom plate to subfloor, etc. Some approaches to double wall framing can reduce this effect, but only if the floor and ceiling assemblies are carried on the inner wall.

    Any type of gasket you use behind the drywall (which also has to happen at the perimeter of all door and window openings and at every electrical outlet) will move the drywall out of plane (create a slight bulge), since no gasket will compress to zero thickness. It is for this reason that I do not use ADA gaskets (available, by the way at behind drywall, only Tremco acoustical sealant.

  2. Brian Mahoney | | #2

    Thanks Robert,

    We have been preparing for ADA during all the construction stages and have already sealed the framing members. Most of these sections have been sealed with high density spray foam. We went with a flash and fill approach with 2" hdsf on exterior of walls (4" on exterior of cathedral ceiling since hitting R60 here) to increase the condensing surface temperature and airseal. When they did the spray foam we had them spray full 10" at the top and bottom of each wall cavity, sealing the top and bottom plates. Also have hdsf in rim joist areas and sealed sill plate to foundation...

    I know this is not the way you normally do this (I took your course and had deep discussions at picnic table!) but found an approach that me, builder and inspector were all ok with.

    We are not planning on polyethylene and will need to use appropriate perm paint for vapour barrier.

    I will look at the gaskets from conservation technology.

    Any concerns about the drywall installation? Anything you may do different given the stage we are at? Thicker drywall, longer screws, etc?

    Do you think the slight bulge from gaskets is a significant concern?


  3. Riversong | | #3

    Do you think the slight bulge from gaskets is a significant concern?

    Perhaps not, since it sounds as if there may be bulges from the insulweb/cellulose. Maybe it will all be at the same plane?

    My primary issue with the drywall gaskets is that it can alter the angle sufficiently at the bottom of the wall to make clean baseboard miters difficult. But, if you're using paint-grade trim, that may not be an issue. I also don't know how well any gasket is going to seal to the plates where insulweb is stapled on the surface. I would think that Tremco would seal a lot better.

    If you're framing is 16" oc, then ½" DW should probably screw in tightly without bulging. But if you're at 24" oc, then you might need 5/8 rock. Try a sheet or two and see what happens.

  4. Aj Builder, Upstate NY Zone 6a | | #4

    Even subfloor glue would do the job no?

    In any event.... am jealous... sounds like a great build.

    Sqft, location, heat system,size,load & expected annual btu?

  5. User avatar
    Michael Chandler | | #5

    We take a 24" chunk of 2x6 and drive 16 D nails in the corners then drive three utility knife blades into one end at a 45 degree angle, feed 6" sill seal down it and pull it through into a trashcan to make four strips out of a six inch roll. staple it to the lower top plate after the ceiling is hung but before the walls are hung with a slap tacker. no worries about extra nails on the sheetrock there but do remember to have them not fasten the ceiling to trusses within 18" of the interior walls to minimize cracking due to winter truss uplift.

    You can see some pics here:

  6. Brian Mahoney | | #6

    House is in Kingston Ontario. In heritage district, Cape style with 3' knee wall upstairs with dormers. Around 2800 sq ft. R-20 subslab, R-10 slab edge, R-20 below grade walls, R-40 above grade walls, R-60 cathedral, R-80 ceiling. Windows triple glazed, fiberglass, krypton filled and tuned, south facing has higher SHGC.

    Calculated heating load was 48000 Btu/h. The guy was surprised, said great job, 20% below what code built house would be, I did the calculations. I was surprised, assuming it would be much better. I questioned the variables going into the computer simulation and assumed the simulation was not made for a house like this. Forked over my $650 and never got it redone. All hydronic heat, some in floor, some in Runtal wall panels. Calculated the loads in each room based on 160 degree water to meet the 48000 above. My plan is that I will be running much lower water temperatures. Wall hung condensing, modulating Viessman boiler also providing indirect hot water to back up solar thermal panels.

    I wanted the gaskets because the drywallers did not want to do acoustical sealant, glue or anything like that. I did not want to follow them around and wouldn't trust it would get done well if not observed.

    Thanks for the info and technique on sill seal Michael. Your homes look great! I think that is what we will do. Starting to run low on money...

  7. Aj Builder, Upstate NY Zone 6a | | #7

    Super posts Brian and Michael. We all really learn from actual builds and the numbers involved.

    Could you share some costs? Heating system, home, insulation...

    And lastly I hope your actual numbers prove to be excellent.

    Very interesting about the lack of savings with such high R numbers and so much sealing. Do you know your true whole R numbers taking in to account thermal bridging etc?

  8. Doug McEvers | | #8

    A home with these specs should use about 1 btu per square foot per heating degree day. You will have to do the conversion from C to F. This house with 8,000 heating degree days will use about 225 therms.

    Your energy auditor has not a clue about design temp heat loss for this house, i would say the maximum is about 15,000 Btu. Have someone knowledgable redo the energy calculations if you are using this information for sizing HVAC. My numbers assume an ACH50 of near 1.

    I built and monitored 6 double homes with similar specs and the annual heating load ranged from 1.3 to .9 Btu/sf/hdd. Your windows are far superior to what was available at the time I built these homes.

  9. Riversong | | #9


    Doug's estimate should be pretty close. If you took my Efficiency by Design class, then you have the tools necessary to perform an accurate heat loss/heat gain analysis.

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