I’ve heard pros and cons about air sealing attics. I’m looking for pro building science advice for a home we are taking possession of soon. My main concern is making sure any air sealing, HRV installation, and HVAC/duct upgrades are done properly so we do not create depressurization, backdrafting, condensation, or moisture issues.

Home details:
- Approximately 5,050 sq ft
- 10 years old
- Located in Coquitlam, BC
- Hydronic radiant in-floor heating
- Separate ducted AC-only system
- No furnace
- Existing AC ducting is mainly in a low-pitch vented attic, roughly 4:12

Current ventilation/exhaust details:
- No HRV currently
- We want to add an HRV if possible
- Two high-CFM kitchen hood fans vent to the exterior on main floor
- One low CFM kitchen hood fan vent to exterior in basement
- Two dryers, one in the basement and one on the main
- Seven bathroom fans
- One bathroom fan currently runs continuously as our primary fan
- Boiler has dedicated intake and exhaust to the exterior
- Fireplaces are electric

Note, most walls are sheer walls in this home so penetrating most walls is not an option.

What hoping to receive advice on:

How to air seal the attic safely without creating pressure or moisture problems?

Whether the house needs dedicated makeup air because of the high-CFM range hoods, dryers, and bathroom exhaust fans?

How to avoid depressurization issues after air sealing?

How to confirm there is no backdrafting risk under worst-case exhaust conditions?

Best HRV strategy for this house, especially with limited duct routes due to shear walls?

Whether the HRV should be dedicated ducted, partially dedicated, or tied into the AC return?

How to manage fresh air distribution without creating comfort, condensation, or pressure issues?

What testing should be done before and after upgrades?

My goal is to improve energy efficiency and indoor air quality while avoiding unintended problems with moisture, condensation, pressure imbalance, or attic air being pulled into the home.

Thank you!

Last year we dealt with high interior humidity levels (60%) and water spots in multiple rooms from condensation in our attic. These spots grew after rains but a roof leak could never been identified. Starting to wonder if we are dealing with something like solar vapor drive. Anyone have any thoughts?

Backstory. This is a ranch style condo in the center of a triplex. The neighborhood had an issue with lp fire block sheathing that caused similar moisture in the past and was remedied with a waterproof coating similar to dryblock. It’s been determined this coating is failing and no one wants to remove and recoat.

Last year we had attic insulation, and baffles fixed. / added after an insulation contractor determined several baffles weren’t installed properly and wind had moved attic insulation around.

I’ve been doing plenty of research on the pros and cons of putting foam in an old home. My house was built in the 70s and the attic was meant to be unconditioned, vented, and the same temperature as the outside. I’d like to keep it that way.

Currently, however, there is insufficient fiberglass insulation on the attic floor. The attic floor is literally the upstairs unit ceiling – the only thing separating the insulation from the upstairs unit is a thin layer of sheetrock. The attic is not meant to be walked in, and it’s also too narrow to stand up in without the roof off. So I’ll be doing all of this while I’m having the roof replaced.

I live in a climate that gets to -20 Fahrenheit in the winter. The boiler will be running constantly and the baseboard heating can’t keep up with the heat loss. It’ll barely stay at 55°.

A contractor proposed spraying 2 inches of closed cell Spray Foam over the attic floor to seal the attic floor entirely and prevent hot air from escaping into the attic. He would first install baffles in the eves to ensure they remain vented, and after spraying 2 inches of foam, he will add fiberglass insulation on top of it to bring the value up to R-60.

This seems like a phenomenal way to reduce my heating bill in the winter and keep the upstairs tenants warmer, and happier. But I’m not the expert. Are there any major downsides to adding closed cell Spray Foam to an attic floor for the purpose of creating an air seal between the attic and the upstairs unit, particularly to a house that has never had Spray Foam in it before?

Keep in mind, this contractor understands the importance of keeping the attic vented, and will only be putting it on the floor, and nowhere else. He will be installing brand new baffles to ensure the attic retains airflow through the soffits, and my roofer will be adding a ridge vent at the top of the roof.

I recently noticed an area behind a hvac duct that did not have any spray foam installed on it when the house was originally built. The missing spot is on the roof deck behind a hvac duct that was hung from a rafter. Looks like open-cell was used in the house. What is the best route to fill in this missing section myself? Can I use the great stuff cans from the hardware store to do this even though that is closed cell? The missing area is about 1 ft long and 6 inches wide, but it is on the underneath of the roof deck.

I am adding an extension to our forever house here in the East Bay of the San Francisco area. In speaking with our energy consultant who's working on the project, their suggestions was to add 2 in of exterior continuous insulation for thermal performance improvement. However, The ROI is not a near term ROI. (nor the only metric I'm interested in).

I am also interested in creating a more comfortable house and am planning on using mineral wool to further mitigate sound. My objective is to create as comfortable an environment as possible in addition to energy savings.

My architect and contractor are both looking at me like I am crazy and this is a ridiculous waste of money. However, neither of them have experience with this approach.

It's not required by code. I get that from a traditional financial perspective it is not the "best" use of budget.

Personally I would like to go beyond code for energy savings, (the world is only getting hotter) and I'm excited about what I understand to be improvements to the indoor environmental quality of the house.

So am I crazy?

I’m buying a new home and on the inspection I noticed the crawl space is a bit humid. The crawl space has a concrete floor and I was wondering if laying a vapor barrier would be a good or bad idea for it. The crawl space has no standing water with any active leaks. If I lay the vapor barrier would that just create mold on the underside or would the water vapor just not rise through the concrete ?

Hi all,

My wife and I are strongly considering putting an offer on our first (and hopefully only) home. We are both in our mid thirties so ownership timeline is hoping for 50-60 years, and I would like to ensure whatever home we buy is as solid as possible for that time.

The house we are considering is a 1951 build (this is in Ontario, Canada). No known foundation issues (inspection to be conducted) but the previous owner spray foam insulated the basement a few months back. There is no exterior waterproofing of the foundation.

Now I have been doing a boatload of reading and it sounds like spray foam insulating the basement (which acts as an air/vapour barrier) is a contentious topic when the exterior is not waterproofed. I have posted about this on other subreddits with mixed response.

So I thought I would come here and inquire after the consensus. Is spray foaming a bad or potentially dangerous thing in this case? Would it be worth doing a full exterior waterproof of the foundation? How much (specify CAD or USD if you like) would it generally cost to coat, dimple mat, and install a weeping tile, and how much if I do the digging element myself at the very least?

Thanks in advance!