LEED Milestone: Pre-drywall Inspection

Well, we cleared a major milestone on our path toward obtaining our LEED certification, the “Pre-drywall Inspection”.  In the early stages of the design we identified a number of  “green” materials and building techniques we intended to use. An independent third party then uses this list to verify that we have executed the work accordingly.  A large number of the items on this list are mechanical, plumbing, and electrical items; once the drywall goes on, they will no longer be visible – so we organized for Thermalwise (our 3rd Party Verifier) to come to the house when all work was complete and before the drywall was ready to start.  The inspection went well and we passed!

We also took a couple of extra steps prior to starting the drywall that I believe are invaluable to anyone building a new home. LEED or not, I will be recommending to clients that they have the following checks done!

A.  Thermal Imaging

Thermal Imaging – allows one to see variations in temperature. When viewed through a thermal imaging camera, warm objects stand out well against cooler backgrounds. – wikipedia

The following images illustrate how thermal imaging can identify “weak” areas in your thermal envelope… how good is your insulation, and just how thermal bridging can increase your heat loss.  We used the thermal imaging prior to installing the vapour barrier.  This way we were able to come back and fix some of the weak zones.  First, I want to say that I believe we have worked with a great general contractor and subcontractors who have been collaborating with us in this process.  Showing up at the site with the intent of trying to find “problem” areas, I was not sure how everyone would react or what we would find. Here are a couple of things we found – the double stud wall is very beneficial in the reduction of heat loss . Fig. 1 shows the wall assembly at an outside corner.  You will see that everywhere but the corner there is very little heat loss. (What we did learn was that because of the way the walls were framed, the insulating installers could not get the cellulose into the corners.  This was remedied by drilling holes in the stud to blow insulation into the corners.)

Figure 1.

(Note the temperature differential – wall area at about 50 (10°C) with the corner stud at 33 (0.5°C) – That’s a 9.5 degree Celsius difference.)

Another Image below shows the thermal bridging that occurs around the window. This is one of the only points in the walls that there is material that runs from the exterior to the interior. We used ½” plywood around all the window and door openings to tie the two walls together.  I show this image because if you were building a conventional 2′ x 6′ wall this image would represent every 2′ x 6′ stud in your wall.

Figure 2.

(Note that in conventional framing, studs comprise up to 25% of your wall area.)

We identified a number of conditions during this exercise: most were very easy to remedy; some other were not.  In any case, I will use what I learned in the future when I sit down to design the next house.

B. Blower Door Test

A blower door is a machine used to measure the and to help physically locate air leakage sites in the building envelope.  – wikipedia

The other test we ran was the blower door test.  As described in the definition above we decided to run this test prior to installation of the drywall in order to identify and to be able to fix weak points in our envelope.  As part of the LEED requirements, we must have a maximum of 3 air changes per hour when the house is completed.  Air changes per hour is a way to measure the amount of air leakage in a house, which has a direct effect on two major items, indoor air quality and heat loss.  Houses can range greatly – an historic house with no vapour barrier may be as high as 25 air changes per hour or a newer home would most likely be around 5 – 9 air changes per hour.  The house will get tighter once the drywall is installed, a permanent front door in place, all door hardware is on, window trim is installed, etc., but we wanted to be able to make sure we were close to hitting our target.  We came in at 3.4 air changes / hour which was slightly higher than we expected, but we also identified a number of areas to be improved.  So, hopefully after a Saturday afternoon spent with some spray foam and sealant we have corrected all the identified areas.   Below is an image of the blower door test under way.

Well, that describes a couple of extra steps where we learned a ton.  Why?  Because the pre-drywall inspection is a requirement of the LEED process. This formalized process forced us to stop, have another set of eyes review things and gave us the opportunity to improve the quality of construction.



3 thoughts on “LEED Milestone: Pre-drywall Inspection

  1. Valuable lessons! Very neat to see the thermal images, it looks like something out of a movie, where can you rent equipment to do this?

    I had never heard of the Blower Door Test or the term air changes per hour (although it makes a lot of sense). Dad will attest from his recent visit the air changes per hour in my apartment is probably pretty high with the thin windows and bad framing. How did you measure air changes per hour?

    Posted by mitchellmckenna | March 30, 2012, 2:22 am
  2. Sure sounds great to build something you’ll be very happy with later, good luck. Valerie

    Posted by valerie webster | April 18, 2012, 10:31 pm
  3. Hi there, A friend moved there to P.E.I. last year into a house she just seen on the web! She called it an adventure.
    but I was most curious of the price in making a home? I was also considering to do the same as her! Only at a
    lower cost.

    Posted by valerie webster | April 20, 2012, 9:02 am

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