r/buildingscience

I am building a house in the PNW region, roughtly 30" rainfall per year. ICF foundation, SIPs in 1st and 2nd floors. We will be wrapping the house with a WRB.

We are planning on vertical shiplap siding - it will be a natural wood product. I have read quite a bit about siding and many sources emphasize the need to have a "drainage plane" between the siding and the skin of the house. I mentioned this to my contractor and he had a very strong reaction against it. He said that in his many decades of building houses he has never done this, and never had a problem. Furthermore, he has done remodels of homes that are 60+ years old and has found that the "paper" underneath the siding is practically intact.

His conviction is so strong, I am wondering if all the building science literature on this subject is over-engineering.

Does anyone have practical experience on this matter? I.e. When is a drainage plane necessary, and when it is a "nice to have". I know the theory, but curious about actual experiences.

I’m all for modern building science, which might be described more accurately as experimental science or laboratory science. Why this slight name shift? Because the science we are talking about draws principally from rigorous experimental and laboratory testing of a disprovable hypothesis. This kind of science wins when it can be performed over decades. It needs decades because when a disprovable hypothesis is tested only over months or years, it may not have the kind of evidence we want about longevity. Laboratory and experimental science can be paired with statistical and simulation modeling to project what longevity of new technologies will be. But evidence from modeling is not evidence from observation and experience.

There’s another kind of inquiry that ought to be discussed more often. This has been called positive deviance analysis in medicine and other science-based fields. It’s used widely where laboratory or experimental analysis can’t reach, and one of those areas is longevity. How do we know, for instance, that closed cell spray foam won’t be the asbestos of its day? Or that interior vapor barriers in home structures won’t become brittle and fail in 40 years, then rotting wood framing behind it?

You can probably guess that I’m suspicious of the extent of petrochemical building technologies that come from labs and short-lived experience. There is no evidence of how these materials perform over a century. There is plenty early evidence that they pose environmental hazards after a catastrophic event like the Palisades fires. And lots of accumulating evidence of how technical their installations need to be in order to perform like they do in labs.

For evidence on long term longevity, I’d like to see more inquiry into examples we do have, right now, on buildings that have stood straight and performed well already over centuries. Sure, long term survival isn’t the last word on what we want out of a building. Some people prioritize temperature control and comfort. Others want temporary and cheap tear-downs. But some of us do want longevity. I do.

There’s lots to say here, but I’m going to cut this short now and let the Reddit wars unfold.

Here’s my claim.

1. Traditional northern building technologies that have survived did so because they accommodated movement, redistributed loads, and dried well.

Go ahead and rip, Reddit.

I recently replaced the HVAC system in my apartment with a new heat pump install. My old ductwork was poorly sized and wrapped in asbestos, so I paid the contractor to tear out all the old ducting and replace, and add two new vents into two small bathrooms that weren't previously vented.

The contractor finished, a third party came out to run a HERS test, and we passed with flying colors. Incidentally, the HERS testing took about 20 minutes and required almost no equipment....

I then got a call from CHEERS, which is a California's Energy Code compliance group. They wanted to audit the testing - fine. The CHEERS guy comes out, sets up a bunch of tests that definitely didn't happen previously, and gets *nowhere near the numbers reported* by the HERS tester. He didn't want to get into specifics (apparently they're not supposed to share data with homeowners because their role is to verify testers internally) but he mentioned that we will probably see the HERS team again.

My question is: What do I do now? My contractor should fix it, of course, but they're holding a cleared HERS certificate and I have no proof to make them redo it. The ductwork is already behind new drywall, so it's not a simple fix to just retape any joints. The HERS company is obviously fraudulent, but they contracted to the contractor, so I don't even have their info, and now I'm holding the bag with a 18k bill and a poor-quality install that is going to cost me more in the long run even though the paperwork says its fine.... Final city inspection is tomorrow. Of course they rely on the HERS test data so everything is going to pass leaving me with no leverage at all. Should I tell them? How?

Hello all.

I Own a 1923 Craftsman Bungalow home. 

We have applied and been accepted for a grant program to make energy upgrades to our home.

Our climate in the Pacific Northwest, Portland Oregon. 

The grant program aims to make energy improvements to older homes.

They are prioritizing dense pack cellulose insulation 

-We will be receiving a Mitsubishi whole house heat pump to replace a 30 Y/O Natural gas unit + 30 Y/O AC condenser. 

-Radon Mitigation System

-Mitsubishi Heat pump Water heater to replace 17 Y/O gas water heater.

They are working with our wants/needs, but may need to blow in cellulose insulation into the wall in order to hit the numbers. 

This seems to be a highly debated topic, and up until speaking with them I was leaning away from blown in wall insulation due to moisture concerns.

Our wall systems consist of: 

-Original Cedar Bevel Siding

-Tar Paper (it is generally intact, but old, with tears, holes etc.)

-1x10 Sheating 

-2x4 walls

-Lathe and Plaster interior (some drywall in certain areas, but the main areas they would be blowing in insulation are lathe and plaster)

No knob and tube or other concerns on that front.

My main concern was moisture working its way into our wall system, not bulk water, but small amounts either through condensation, wicking, or small areas due to it being an old vapor permeable home.  The worst version of this all in my head is rotting siding, major moisture/rot, peeling paint etc.

Very curious to hear any thoughts on the topic, should I drop my concern and go with the plan? Are my concerns valid? Im open to any perspective. 

Thanks in advance!

*My house needs a scrape and repaint, past owners paint job did not adhere well.

Staircase and bedroom share some wall framing. Im wondering if it would be worthwhile to add mlv to the wall before stairs get framed. Mainly hoping to stop the sound of heavy steps on the treads as the kids run up and down. Will insulate the 2x6 wall as well. Roughly 8 x 16 area so not a ton of material hopefully. Thoughts?

We are looking to buy a new home that has a detached 24x32 garage that we believe was built in 1940. We are in zone 5A. The interior walls are cinderblock, the siding is vinyl, I have not had a chance to look behind the siding, but I assume probably minimal sheathing / no vapor barrier.

I want to insulate this space and add a heat pump so I can use it as a workshop, which includes wall storage for lumber which requires studs to mount to (at least where I put lumber).

From my research I think it makes the most sense to insulate in. I am playing with the idea of adding 2" of foam with taped joints (with tyvek housewrap tape?) glued directly to the block walls and furring strips.

I am also playing with using a thinner layer (~0.5") of foam (still glued and taped) and then doing a 2x4 wall with faced (to the inside) fiberglass insulation. I can't tell if this will prevent moisture from traveling into the fiberglass or merely trap it once there?

Looking for thoughts and idea's for a simple way to make the space usable that won't cause more issues. Thank you!

Originally i was going with EPS basically a DIY SIP panel with foam board and concrete sprayed on the sides, but our spans between walls were too huge so we were told we needed to use block for the ground floor

So how best can we make a concrete building passive? Would we still need an ERV system to bring fresh air in?

The other goal is to make the bedrooms as quiet as possible

Hi all,
We’re currently final stages of planning our passive house build. It’s two stories, 205sqm. North/south orientation, fully sealed with MHRV.

The house is in Perth, Australia, so hot summers and mild winters. Summer can get up to multiple days of 40+, with minimums in mid teens. I’m assuming heating will never be an issue in winter.

We have two options with cooling . Either a fully ducted system on two levels, or just placing units in main areas and allowing the flow to cool down other rooms.

My question is, would option two be enough? we went down the passive house route as we didn’t want to rely on dumping cold air into the house constantly, rather just to need to take the edge off. But there’s also an issue of ‘if we don’t fit it during the build, it’s extremely hard to retro fit.’ However, I’m not convinced a fully ducted air conditioner system (16kw or so) working at a fraction of its capacity is good use of resources and money.

Happy to hear your thoughts, especially those in similar climates. Happy to provide plans via DM if you’d like

Our build was specified with exterior sheathing and then a layer of continuous exterior insulation. Builder is switching to the Zip R system (R-9) which is equivalent to what was specified. I didn't think much of it until I realized that the insulation would now be on the inside of the sheathing, vs being on the outside. I know the Zip system gets lots of praise, but just want to make myself aware: Are there any things to watch out for or disadvantages to this approach. We're in zone 6b if it makes a difference. THANKS!

Hey everyone. I own a 1970s Panabode cottage in Ontario. The structure is comprised of 2.75” thick T&G milled logs. The last two years I’ve lived at the cottage during winter (down to -30c) and noticed quite a few issues.

Substantial heating bills with the propane furnace running 8+ hours a day in January. Warm air venting to the outside through tiny gaps in the log joints and top wall log/eave transition and causing exterior frost build up.

I spoke with some log builders in the region and they advised on doing an exterior energy retrofit and I wanted to get everyone’s opinion on the plan:

The house is on piers. Crawl space is conditioned and insulated with exterior wall spray foam insulation. The roof is vaulted and the decking is 2” thick cedar T&G. The roof boards extend past the eaves (so there is no soffit). There is 6-8” thick batt insulation on top of the roof boards. Not sure if there is a vapor barrier on top of the roof boards (maybe tar paper?).

1. Seal every log joint with log caulking. Larger gaps will have backer rod installed. Especially the wall/eave gaps and log tail joint details. Was also thinking of adding butyl flashing tape on the wall edges to protect against seasonal log movement: corners (lapping log tails), Top where the wall meets the eave. Interior corner joints as well.

2. Remove windows one by one (currently installed in the 2.75” thick log profile) and buck out 2x8 window frames with proper flashing. The window frames would allow for log movement by using a slide (angle iron embedded in log ends on the sides of the window opening, and the 2x8 frame secured to the metal)

3. Install 4” T&G XPS panels (R-20) directly against exterior log face. Seal all gaps with tape, add flashing tape where required. Bottom of the walls will need custom metal Z flashing

At the top of the exterior walls, the XPS will butt directly against the cedar roof boards at the eave.

3. Install tyvek water barrier. Tape seams.

4. Install rainscreen: 1x4 vertical strapping 16” OC using 6” timberlok screws. Cedar shiplap installed on the strapping.

Does this sound like a reasonable plan overall? Any advice would be appreciated!