We live in a vacation home built in 1979, the house is on piers, built on a rock with varying heights (300-1400mm from ground to subfloor), uninsulated crawl space that is partially open for the weather to blow in. Naturally, we have ice-cold floors, so cold that I crawled under the house with a thermal camera, found that at zero degrees outdoors, the underside of the subfloor is 7-8 degrees. All heat in the house goes out through the floor.
There are gaps everywhere in the subfloor, ranging from 1mm to 10-14mm. In one of the gaps, I could measure that the insulation in the floor is at most 145-160mm.
So my two questions are simple.
1. Can you add insulation directly to the existing subfloor? Add 120-145mm, frame new, install mineral wool, asphalt board on the outside. Seal everything with extra insulation.
2. Or should one focus on enclosing the entire crawl space, leveling the ground with gravel, sealing the foundation from ground moisture, and allowing the poor subfloor to heat the foundation.
There are gaps everywhere in the subfloor, ranging from 1mm to 10-14mm. In one of the gaps, I could measure that the insulation in the floor is at most 145-160mm.
So my two questions are simple.
1. Can you add insulation directly to the existing subfloor? Add 120-145mm, frame new, install mineral wool, asphalt board on the outside. Seal everything with extra insulation.
2. Or should one focus on enclosing the entire crawl space, leveling the ground with gravel, sealing the foundation from ground moisture, and allowing the poor subfloor to heat the foundation.
Yes, it is possible to add more insulation directly on top of the existing subfloor.
It is extremely important that it is absolutely windproof, otherwise the cold outdoor air will pull up through the floor regardless of how much insulation there is. Seal the existing subfloor tightly and also preferably add windproof paper under the current subfloor before the new layer, which of course also must be carefully windproofed. (It can never be too windproof, and it's wind-/draft-proofing NOT moisture-proofing.)
I probably wouldn't add too much extra insulation. Definitely not more than 95 mm max. Possibly if the cabin is in a windy area far north where it is really cold in the winters, like in the alpine region, then I would consider more. Cold floors are usually due to drafts caused by insufficient windproofing.
It is extremely important that it is absolutely windproof, otherwise the cold outdoor air will pull up through the floor regardless of how much insulation there is. Seal the existing subfloor tightly and also preferably add windproof paper under the current subfloor before the new layer, which of course also must be carefully windproofed. (It can never be too windproof, and it's wind-/draft-proofing NOT moisture-proofing.)
I probably wouldn't add too much extra insulation. Definitely not more than 95 mm max. Possibly if the cabin is in a windy area far north where it is really cold in the winters, like in the alpine region, then I would consider more. Cold floors are usually due to drafts caused by insufficient windproofing.
Hobby electrician
· Stockholm
· 698 posts
What does "wind-proofing NOT moisture-proofing" mean?Oldboy said:
It should be wind-proofed but no moisture barrier, i.e., wind paper/asphalting paper or wind fabric, but not building plastic. Asfaboard is relatively windproof if all joints are made against studs and tightly nailed, stud spacing max cc 60 cm.
(Any moisture barrier should be on the warm side, i.e., directly under the floor. Which in existing houses requires the floor to be broken up.)
(Any moisture barrier should be on the warm side, i.e., directly under the floor. Which in existing houses requires the floor to be broken up.)
Have the same problem except there are no gaps in the subfloor. But when it’s windy, the floors get really cold. Considering putting a "skirt" with slats between the foundation posts on the outer edge and that type of wind fabric used in animal barns. Such a fabric is supposed to remove 85% of the wind but I have no idea if there are better ways 😁
The wind increases the air exchange in the house, where fresh air is apparently drawn in through gaps in the floor. The wind extracts air through gaps in walls and the roof as well as possibly through the chimney and ventilation duct. This creates a negative pressure in the house, and due to the thermal effect, the negative pressure is always greatest at the bottom. Then, no wind barrier for the foundation helps; instead, it's the floor joists that must be wind/air blocked.
A wind barrier under the sub-floor, as suggested by fribygg, is a significantly more effective measure. It must, of course, be carefully sealed at all edges, joints, and penetrations to achieve the intended effect.
A wind barrier under the sub-floor, as suggested by fribygg, is a significantly more effective measure. It must, of course, be carefully sealed at all edges, joints, and penetrations to achieve the intended effect.
I screwed up 100mm "frigolit" straight up with long screws and a large washer. Foam sealant between the sheets. Turned out great and windproof.
Straight edges.F fribygg said:
That will probably turn out well!F fribygg said:
The reason I bought something that looked like styrofoam was that they were available in sizes around 1200x2400mm.
But they were ground boards.