Cold first floors in a mountain house
We have a ~ 3000 sf vacation house at 4000 ft elevation in the Cascades. The two story house is 30 years old built on a continuous pour perimeter concrete foundation wall with vapor barrier over the earth. In the spring there is 3-4” of water under the vapor barrier from the snow melt. The subbasement is dry in the winter, fall and summer. There is no evidence of rot or mold on the 2 x 14 joists or posts. Conditioning this sub-basement seems quite impractical, given the water issue. I think about this problem like insulating a cantilevered floor, or a floor over a carport.
The bedrooms on the first floor are cold. The existing subfloor insulation is fiberglass batts, installed properly. The top floor is heated by a wood stove. There are in-wall forced air electric heaters throughout the house for supplemental heating.
One suggestion is closed cell spray insulation. I have read some posts suggesting that ccSF will absorb water over time. And other posts that assure that it is an excellent vapor barrier and I should have no concern. If this should prove an insufficient solution, then it would be a lot of work to improve. Does anyone have an idea how I can experiment to decide whether foam insulation is an adequate solution to this problem? I have considered buying a tank of foam, and doing a small area under a hallway and measuring the floor temperature with an infrared temperature gun.
A second suggestion is to install staple-up pex hydronic heating with aluminum plates plus improve the subfloor insulation, either with spray foam or with rigid foam insulation. We have no natural gas. We do not have propane for other utilities. Given a few weeks usage in the winter, a small electric hydronic boiler is affordable. I worry about noise from the heating system. And it is obviously more money and trouble.
What do you experts think of my proposals?
Replies
hyrdronics/foam is an excellent combination that will surpass your expectations (when properly sized and installed).
the concern I would have with this is the time it will take to get the system running and temps up to desired levels if not left on while not in use.
closed cell foam MAY abosorb some miniscule amount of moisture over time but its benefits far out way any concerns the fiberglass guys still push.
depending on manufacturer, you obtain vapor barrier requirements with 1.5''-2'' of foam. Just foaming will help keep the conditioned space conditioned but it will not "warm" your floor.
If the conditioned space temp is not a problem, just the cold floor...hydronics is the way to go.
Hydronics quicker than you think
I found this out when I lived in a 'garden apartment' set into the earth. That is, it was a 2-bedroom apartment that had the windows at grade level. My time there included a couple of exceptionally cold Chicago winters.
The heat was hydronic, set in the concrete foundation. When away, I often turned the thermostat all the way down to the 55 minimum.
My point is that I could feel the response within fifteen minutes. Within half an hour, I was comfortable anywhere.
This had me curious. I took temperature measurements, and discovered why the heat was so "comfortable." Here are the reasons why:
First, the even heat from the floor tended to prevent 'drafts' from forming - even though the windows of this place were the cheapest single-pane, aluminum frame imaginable.
More importantly, defying the laws of physics, the warmest air was near the floor. Your feet were warm. Warm feet = warm you. When sitting, you were below the level of the thermostat - and thus sitting "closer to the heater."
First question is what sort of air infiltration barrier is there below the fiberglass? I know it was the style back in the 60s and 70s to install batts that were open to the crawlspace below, with no air barrier -- don't know if this had changed by the time your house was built. This allows air to freely flow through the batts and totally negates the insulating value of the fiberglass. A simple fix is to staple housewrap across the bottoms of the joists.
3-4" water....
U need
3-4" water....
U need drains before anything else....
Conditioning a "sub-basement", huh? Is that like conditioning one of those over-attics?
Two weeks out of the year? I think your best bet (2nd to fixing that drainage issue) is to just keep the wood stove stoked while you're there. Set a few bricks on its top during dinner and them give 'em to your 1st floor guests when they retire for the night.
well you have graduated
from numb/dumb to plain ol' stupid nuts. Conditioning a sub basement ???? with radiant heating for the first floor???? WOW Sonny, you should REALLY think before you type.
Air infiltration barrier: Kraft paper facing on the batts, facing down, stapled to the joists.
There is no way to drain the water when the snow first melts. There is no location that is at lower elevation except for a nearby creek. Discharging water into the creek is not permitted. Pumping the water into the septic system would overwhelm the system because any water that is removed will simply lower the water level in the sub-basement to be immediately replaced by nearby snow melt.
Thanks for your suggestions. Will discuss with a hydronics expert.
It would be rare for kraft paper, installed that way, to be very tightly sealed at the seams, unless they are taped.
This is what I learned from a hydronics expert:
If you want to experiment with insultation, bring up some 2” rigid foam boards and lay them under the bottoms of the joists with sealant. If this helps noticibly in one region, perhaps it is enough. Won’t make the floors warm. If the improvement is sufficient, then the best solution is probably to blow ccSF unless you want a DIY project in which case he recommends foamboard laid against the decking, then batt, then taped foamboard at the bottom of joists.
The optimal solution will be hydronic plus better insulation. You can add hydronic on top of the existing floor (1.5” of gypcrete leveling cement with PEX tubing). Then you can finish as you wish. Some people leave the gypcrete. Some give it a colorized concrete look. Others top with Pergo (1/2”) or carpet. The doors and stairs may require some adjustments. OR you can add hydronic on the bottom of the floor. The aluminum plates are really expensive. But it avoids the change in floor height. There is no noise with hydronic in gypcrete. There are ways to mitigate noise with aluminum. Definitely have a pro size the boiler and do the controls. It may be the same cost to put hydronic above or below the floor.
The boiler will need a lot of juice. Have to look at the service. 200 A may not be enough. It is not small with the pump and other controls.
It takes at least 12 hours to heat up. So, you probably want a way to remotely control the temperature with a wifi thermostat.
Separately, you should put a humidistat controlling two vent fans in the basement. The fans sit behind the vents. That will keep the air moving when there is water in the crawlspace.
Some Thoughts
Your concern about closed sell foam absorbing water over time are unfounded. More likely you'll get a strange look from the foam guy for your request - but he;ll happily spray fo pay!
Simply closing off the joist spaces might give you some help- but I doubt it will be enough.
Don't overlook the top face of the floors. Additional floor coverings - carpet, rubber tiles, etc .... can make a pretty big difference. I discovered this when I put 3/4" thick "stall pads" on the floor of the room I use as a gym. I mean- it's mid-winter here, and the cat is happily napping in a cardboard box on that rubber mat!
How's your airflow under the house? Wide-open crawl space vents can really cool a floor. Self-regulating vents will close at freezing. They made quite a difference to my floor.
I agree that your drainage needs to be addressed.