Hardwood floors in a Passivhaus
Passivhaus question: Do hardwood floors contract and gap in winter as noticeably as they do in a conventionally-built house?
My husband and I are building a Passivhaus in Vermont and want to install hardwood floors. I’m tempted by pre-finished flooring, since we wouldn’t have to go through the mess and expense of sanding and finishing on-site. But I hate the little dirt-strips that inevitably form in the micro-beveled edges.
We were therefore planning to install unfinished hardwood flooring and have it finished on-site, but a builder friend pointed out that even site-finished floors will develop gaps (and dirt-strips) in winter when the floorboards contract.
Is that likely to happen in a Passivhaus? Our house should be less dry in winter than a conventional house, since we won’t need to heat the air very aggressively. How much humidity fluctuation can floors withstand before forming little gaps?
I’ve never actually been inside a Passivhaus, so I’ll appreciate hearing from those of you with more experience.
Thanks!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Andrea,
Have you considered an engineered floating floor? Because they expand and contract as a unit, they are much less likely to develop seasonal gaps.
We are building a passivhaus Arlington, VA. We plan to put in pre-finished bamboo flooring. Our consideration between pre- finished v.s. site-finished was less about the gaps. I have pre-finished bamboo in my house and I am typically the one sweeping. I don't notice dirt getting trapped, it always gets picked up with my broom. I know because I actually get on my knees and wipe the floor (an old habit developed from growing up in Asia).
I imagine there will still be some level of expansion and contraction with whatever wood you use. I think the more serious concern is whether site-finishing will leave you with a lot of VOCs. If you choose to site-finish, you probably want to use zero-voc products. Also the ERV registers should be taped up. Same goes for pre-finish too actually, wince there will still be lots of cutting going on on-site. But I think pre-finish wood has had the time to off-gas a lot longer and at a place that is not your air-tight passivhaus.
My guess is that a passivhaus will not behave that much differently than a regular house in this regard. I live in a very tight house in VT that is very close to the passivhaus standards. We have experienced what I would estimate are fairly typical fluctuations in humidity over the course of a year. Ultimately, the air in the house comes from the outside. That air is going to be dry in the winter and humid in the summer unless you are doing something to treat the air coming in, e.g. an ERV.
Andrea,
There will be differences in the interior relative humidity from summer to winter, even in a Passivhaus. However, these differences don't destroy hardwood floors. In most cases, any cracks are tiny, and the dirt accumulation problem you mention is insignificant in most houses.
I think a drafty house is usually MUCH dryer in wintertime than a well sealed and deliberately ventilated house. The wood will shrink because the house will be dryer in winter than summer but not as much as in a "typical" house. The nice thing about finishing on-site is you get to use American-made, even locally harvested, materials as well as labor, you have better control of the finish used, and you can avoid more noxious products. The downside is as you have stated, dusty and smelly, but not that much different in price from a good quality floating floor. Check real costs, you will be surprised at how expensive a manufactured floor is once it's installed.
Michael, I think you've summarized it perfectly. And thanks everyone for responding! We probably will go with a site-finished floor, and we'll choose a low-VOC finish from GreenSpec. Being in Vermont we have a lot of good local sources for flooring (although the engineered stuff from Maine and Quebec is relatively local).
Roger, thanks for the suggestion about taping the ERV registers. We should probably throw open the windows for the initial air-clearing, and then rely on the ventilation system for the ongoing phase.
I live in a house built to PassivHaus standards with hardwood flooring. It was site finished and sealed using a low VOC sealer. It is a hickory floor and we have lived in it for 15 months and in areas with intense sunshine we have seen tiny gaps open up. We live in Utah where the ambient humidity is low, however the humdity inside the house stays within the "normal" range on our "inside weater monitor". I had the exact same floor in a conventional house and saw about the same amount of shrinkage over time.
I do most of the mopping duties, and so far it hasn't created any clean up issues. We might have experienced more shrinkage as we do use radiate heating.
Especially since you're already in Vermont, I'd strongly recommend finishing your floors with Vermont Natural Coating's Poly Whey. We've used it on a couple of jobs and I'm very impressed with the finish. I walked into the house while it was being applied and didn't even know there was open poly in the house.
And I love beat up old floors with gaps. I always tell my clients it takes about 20 years for a hardwood floor to really look good.