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Building Gaskets and Air Sealing Tape

by Chad Ludeman on October 30, 2009 · 12 comments

in Building Science,envelope,materials,Passive House

Yesterday we looked at some lessons learned from our aggressive air sealing goals on the Passive Project. In doing so we mentioned that we will be utilizing building gaskets and air sealing tape to help obtain the very difficult building air tightness goal of 0.6 ACH @ 50Pa that is required by the Passive House standard. Let’s take a more detailed look at the technology and economics of these two construction materials that are less than standard in the average US home.

Building Gaskets vs. Construction Adhesive

Over in Germany where the Passive House standard originated, they have been using rubber building gaskets for over a decade rather than typical construction adhesive that is used in the US building industry. These gaskets are usually made of EPDM and are similar to the ones used in automotive applications. These gaskets offer a far superior seal for water and air infiltration in difficult and uneven joints like wood to concrete and even wood to wood connections.

I just stumbled on a company in Baltimore, MD – Conservation Technologies – that carries a whole host of these German inspired building gaskets, along with a whole bunch of other cool building products for earth loving projects. They have a whole list of reasons why their gaskets are better than caulk or foam that is typically used in the US. Below are the Pros and Cons that we see:

Pros of Building Gaskets

  • Superior seal to caulk and foam gaskets or adhesives for both water and air infiltration, especially on uneven surfaces.
  • Gaskets will last forever with no deterioration.
  • The installation is easy to perform and easy to verify whereas caulk or smaller foam gaskets are very difficult to verify proper application once the walls are secured in place.

Cons of Building Gaskets

  • Cost premium (see below for analysis)
  • Limited availability
  • Construction crew resistance to new technology that is clearly awesome and being used in the rest of the enlightened world for the past 10+ years.

Cost Analysis of Building Gaskets vs. Construction Adhesive

I’ve compared the raw material cost only of two applications of the gaskets. The first is a gasket that would go on a 2×4 to be used at a sill plate location or between the first and second floor of a house. The other is an interior application at the drywall to wood connections. It’s clear that the cost is 2-3 times that of conventional construction adhesive. Some may claim this is expensive, but I was happy to see that the cost difference was not much higher.

2×4 Building Gasket = $0.44 per linear foot
Double Construction Adhesive = $0.15 for two lines per linear foot (1/4″ beads with 10% waste per tube)

Drywall Building Gasket = $0.16 per linear foot
Single Construction Adhesive = $0.075 per linear foot (1/4″ bead with 10% waste)

If we were to take one of our standard building footprints of roughly 18′x40′ that would mean our perimeter is 116′. We would use at least three instances of the 2×4 gasket at the sill plate, second floor and roof details for a total of 348′. Using gaskets rather than a double bead of construction adhesive would add roughly $100 to our material costs. Not bad at all for extreme confidence in a good number of our critical air sealing junctions. Not bad at all.

Air Sealing Tape Analysis

OK, we’ve looked at gaskets, now lets look at using a whole bunch of tape to seal the seams in our sheathing prior to installing our WRB. This seems extreme to most, and maybe it is, but man does it look good. It also seals a building up really nicely for very little additional non-skilled labor. I mean, we can all handle a roll of tape.

Taped Sheathing Seams Image

Passive House people love this Grace Vycor Tape for their OSB air sealing. I’m sure there are many other butyl based tapes out there that are similar and just as effective, but we will use Grace Vycor for our example. It can be found online in 6″x75′ rolls for about $24 which is not cheap, but certainly is not a bad deal for such a lovely product.

Our homes are small and infill, so we have two facades that are roughly 18′x25′ to be taped. This equates to 900 square feet with roughly 12′ of tape needed for each 32 square foot sheet or sheating (only two sides need tape as the others will overlap other sheats). This gives us $337 of tape needed. Let’s go ahead and round that up to $500 for extra tape needed on corners, windows and door openings if we are so inclined. While this is more expensive than the gaskets, it’s still manageable and should go a very long way to reducing air infiltration in our homes.

So there you have it. For less than an extra $600 in material costs and negligible labor additions, we have created a very air tight envelope that is easy to inspect and verify. Your costs in detached homes will obviously be larger, but they should still be in line percentage wise with your build costs as you are already used to buying more sheathing, cladding and the like. Offer your thoughts on these material additions to traditional builds in the comments and thanks for reading.

If you enjoyed reading this post I can promise you'll love our new writing over at Postgreen Homes. Yeah, we know that's the same thing your favorite band said and their new album is nowhere near as good as their early stuff, but seriously, we are actually still getting better.

There also isn't much conversation to be had here . . . at least not with us. So come on over to the Postgreen Homes Blog and tell us what you think of our new(ish) digs and crazy ideas. We will be sure to tell you what we think of your opinion.

{ 2 trackbacks }

building gaskets | Root Design Build - Green Homes
August 30, 2010 at 1:43 pm
Framing in LEED house in Fishtown
October 13, 2010 at 1:30 pm

{ 10 comments… read them below or add one }

1 darin October 30, 2009 at 3:24 pm

Great post and cost analysis! It’s always amazing how many times someone will say something is ‘too expensive’ when in reality it’s the same as a few tanks of gas (for a large truck).

2 chad October 30, 2009 at 3:26 pm

Excellent point Mr. Darin. Excellent.

Let’s build all of our homes faster and more efficiently, and throw the saved gas dollars on more gaskets, tape and caulk! Fantastic.

3 goran November 4, 2009 at 4:16 pm

Chad, thanks for that post. Its tough not meeting the air sealing objectives on the Passive House projects, but it looks like you’ve done a very good job of turning it into a learning experience, and turned it into a step forward for PostGreen becoming a premier Green builder.

I had been thinking of engaging ISA to a Passive House redesign of our home in NJ, but held off because I couldn’t find a builder I was confident could build the project to specs. It looks like this is actually much tougher than I’d thought. Your post gives us information that can help select a builder in the future.

I was wondering whether it would be possible to create financial incentives for construction crews to meet infiltration targets? I’m guessing its not. The construction crews are going to rely on you (and the architect), to provide them with techniques to do the sealing. If the techniques they’re provided doing work, its difficult to say whether its because: the techniques are inadequate, the skill levels required for the techniques to succeed are excessive, or the construction crew is not conscientious. And its not fair to crew if its one of the 1st two. The problem is, there are no construction standards yet for the levels of air tightness you’re trying to achieve.

Good work.

4 Jesse Thompson November 5, 2009 at 12:04 pm

Goran,

You can offer financial incentives, and it can work well. What we have seen several times now is that crews who have not worked on a well air-sealed project generally grumble at first and are worried about looking bad with a process they haven’t tried yet, but once they get involved in the air sealing process, they end up with a huge amount of pride in the end at hitting the target.

Framers especially don’t have much opportunities to boast since their work gets hidden so quickly, but they are the crew who carries most of the air sealing weight. On the last few projects lately the PM ended up telling all his friends about the CFM50 they hit every chance he got, and showed up for the blower door test early to make sure they didn’t look bad. It’s great to see, they get converted really easily and because air sealing in rough framing is actually a fun process, it’s like detective work.

Trying to hit 0.6 ACH50 on the first attempt with a new crew would be very difficult, but 1.0 or 1.5 ACH50 is very attainable with new construction.

Jesse Thompson
Kaplan Thompson Architects

5 chad November 26, 2009 at 1:04 pm

We’re thinking of hosting a party after rough framing is complete for the crew if we hit our initial air-sealing target. It’s our firm belief at Postgreen that good food and beer can be a better motivator than just plain old cash (that the actual workers may not even see).

This could also be a chance for the framing crew to invite some family and friends to see their work and accomplishment, which I doubt happens very often in their field.

6 Jim C December 11, 2009 at 7:17 am

Chad, my builders will be putting up tyvek and window flashing next week on 6 inch sip house. Did you seal all of your sip panels on the interior or exterior seams? 4 or 6 inch vycor flashing tape? I want to tape all the sip seams before the tyvek, I’d prefer to tape the exterior.

7 chad December 11, 2009 at 10:09 am

I would recommend taping the exterior seams and then Tyveking over and taping those seams. What size Vycor you use is up to you, but I’d probably go with the 6″ for minimal upcharge. The larger size will also be more effective if you are also using it to flash your windows and doors.

As important as these measures, if not more, is ensuring that your framing crew is following all of the SIP manufacturers details to a ‘T’. Using the correct amount of construction adhesive and correct joining methods is critical to getting the most air tightness out of your SIP structure. If your crew is cutting corners here, you are losing a lot of the value of SIPs from day one…

Good luck!

8 Mike Schettine May 14, 2010 at 5:10 pm

We combine the 16″& 24″ stud layout on a gasket that seals the entire envolope in the same pass…Gaskets have proven to be effective but they were dismissed because they slow down the framing crew. Now they have a reason to use AccuFrame Zap-Gap
because they get both speed in layout and quaility control as our stud layouts has two lines with X to locate the stud…no more, “he studs on the wong line stuff”

9 Kris December 7, 2010 at 2:20 am

My understanding is that SIPs should be taped on the inside seams since the SIPs are acting as your interior vapor barrier they need to be tightly sealed at all seams and where you install electrical boxes or other penetrations.

10 jon February 25, 2011 at 3:20 pm

The Vycor system looks cool, and it’s advantage is that the shell can stand raw to the weather for a few months, if need be. It also theoetically allows you to avoid having to install vapor barriers on the exterior, or ice and water shield on the roof. But most builders won’t trust the product to perform successfully, so you wind up with two layered systems.

In heating climates, I’d be very concerned about using and exterior sealing tape. You want a tight air barrier on the interior of the house, and assume that moisture will get into the walls and need to migrate out. If that moisture can’t get out, you’re likely to have mold or rot starting behind the sheathing, where you won’t discover it until a great deal of damage is done.

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