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Question DetailsAsked on 8/21/2016

About weather proofing concrete sun room floor. The room is 12x20, concrete slab with 7 screen openings.

I want to insulate the concrete floor so that once the windows are installed it will be a year round room. I am trying to find a DIY affordable solution

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2 Answers

0
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With a slab on grade, you have to be very concerned about moisture coming through the slab into the flooring materials, so you have to either stop the mosture at the slab, or allow for dissipation into the house.


Here is a response on a similar situation I answered yesterday which might help understand that issue better -


http://answers.angieslist.com/I-7-12-...


Simple solution to your case ASSUMING there is no risk of water overflowing this slab in the future - vapor barrier over the concrete properly sealed at the base of the walls (which could be insulated vapor barrier padding - looks like bubblewrap but does not pop as easy) with water-resistant (synthetic yarn and backing) thick but breathable carpet over it. Synthetic yarn and backing to reduce risk of mildew/mold, and breathable to dissipate and moisture either escaping from the slab/vapor barrier or from the house trying to condense on the top of a vapor barrier on really cold days when this room might get pretty cold.


For a higher level of insulation, depending on elevation of the slab versus adjacent room in house because you do not want to put a water-shedding surface above your house foundation or adjacent floor levell just in case of wall or roof leak into this room. You could glue-down (with construction adhesive, glued to prevent "slap" when walking on it), extruded polystyrene closed-cell foam board like Dow Hi-40 with seams sealed with adhesive as well, covered with glued-down Type X (fire resistant) concrete backer board with cement-based joint sealer (to meet fire code because foam board cannot be exposed to potential interior fire sources), vapor barrier possibly, then a floating floor (preferably pure vinyl) or carpet over that. Insulating value of concrete backer board near zero to 1, R-value of foam board about R5 per inch. One inch will give a noticeably warmer floor - "feel" roughly equivalent to a thick carpet, 2 or more inches will generally eliminate the cold floor feeling to all but bare feet. If joints in insulation board are smooth and sealed with adhesive to be airtight, vapor barrier should be left out to avoid having two vapor barriers in the layers.


Another alternative - a built-up insulated floor like discussed in the above question link. The reason batt insulation over vapor barrier was recommended there instead of board is board insulation acts significantly as a vapor barrier, but would not be present under the framing - so you end up with the underlying moisture getting into the framing and rotting it, even if treated wood as it should be in this situation. The unfaced (no paper or foil) fiberglass batting allows significant moisture penetration and dissipation through the wood flooring and connections (in that case) with the rest of the house, which you would not get with either board insulation or concrete backer board.


In both these cases, pretreating the concrete with a good moisture barrier sealer would help limit ground moisture penetration and risk of mold, but have to be sure it is not going to be a type (like some silicone ones) that will keep the insulation adhesive from sticking if using foam board. If using batt insulation and built-up new floor, still use a vaapor barrier over the concrete even if sealed, because most sealers inhibit moisture passage, not really a true "vapor barrier" as much as a "vapor retarder".

Answered 2 years ago by LCD

0
Votes

Note - for some reason start and end portion of reply got cut off - ignore first post and use this one:


One consideration - check building code - in many areas with any frost penetration you cannot legally do this without a legal depth (typically 2-6 feet depending on area) foundation under it. In others you can, but cannot have any rigid connection to the house so it will not damage it during any frost heaving. So check first (or make sure architect does if using an architect for this) so you don't find out you have a non-conforming and unsaleable house come sale time.


With a slab on grade, you have to be very concerned about moisture coming from the ground through the slab into the flooring materials, so you have to either stop the moisture at the slab, or allow for moisture dissipation into the house.


Here is a response on a similar situation I answered yesterday which might help understand that issue better -


http://answers.angieslist.com/I-7-12-...


Simple solution to your case ASSUMING there is no risk of water overflowing this slab in the future - vapor barrier over the concrete properly sealed at the base of the walls (which could be insulated vapor barrier padding - looks like bubblewrap but does not pop as easy) with water-resistant (synthetic yarn and backing) thick but breathable carpet (with or without breathable padding) over it. Synthetic yarn and backing to reduce risk of mildew/mold, and breathable to dissipate any moisture either escaping from the slab/vapor barrier or from the house trying to condense on the top of the vapor barrier on really cold days when this room might get pretty cold.


For a higher level of insulation - depending on elevation of the slab versus adjacent room in house, because you do not want to put a water-shedding surface above your house foundation or adjacent floor level just in case of wall or roof leak into this room. You could glue-down (with construction adhesive, glue is to prevent "slap" when walking on it), extruded polystyrene closed-cell foam board like Dow Hi-40 with seams sealed with adhesive as well, covered with glued-down Type X (fire resistant) concrete backer board with cement-based joint sealer (to meet fire code because foam board cannot be exposed to potential interior fire), vapor barrier possibly, then a floating floor (preferably pure vinyl) or carpet over that. Insulating value of concrete backer board near zero to 1, R-value of foam board about R5 per inch. One inch will give a noticeably warmer floor - "feel" roughly equivalent to a thick carpet, 2 or more inches will generally eliminate the cold floor feeling to all but bare feet. If joints in insulation board are smooth and sealed with adhesive to be airtight, vapor barrier should be left out to avoid having two vapor barriers in the layers. And again, a breathable carpet pad and carpet is much better than a floating sheet or laminate flooring because it will allow moisture dissipation and not act as a second vapor barrier, though if the foam board is smooth cut and fully sealed at the seams I would be less concerned about that than otherwise.


Another alternative - a built-up insulated floor like was discussed in the question link above. The reason batt insulation over vapor barrier was recommended there instead of foam board is board insulation acts significantly as a vapor barrier, but would not be present under the framing, only between them - so you end up with the underlying moisture getting into the framing and eventually rotting it and/or molding, even if treated wood as it should be in this situation. The unfaced (no paper or foil) fiberglass batting allows significant moisture penetration and dissipation through the wood flooring and connections (in that case) with the rest of the house, which you would not get with either board insulation or concrete backer board.


Note I did not talk about using polyiso type board - which can have an R factor of up to 8 per inch - because I just do not trust that type of product in an "interior" application without a vapor barrier between it and the living space - too much risk of poisonous gas dissipation into the house. Plus, it loses its R value over time as the encapsulated gas bubbles diffuse, so over the long run much better than polystyrene board.


In both these cases, pretreating the concrete with a good moisture barrier sealer would help limit ground moisture penetration and risk of mold, but have to be sure it is not going to be a type (like some silicone ones) that will keep the insulation adhesive from sticking if using foam board. If using batt insulation and built-up new floor, still use a vapor barrier over the concrete even if sealed, because most sealers inhibit moisture passage, not really a true "vapor barrier" as much as a "vapor retarder".


One other thing you can do to help with the cold floor situation if in an area with winters (so outdoor soil drops into the 40's or below for extended periods of time) is to dig down 2-4 feet and put closed-cell insulation board on the outside of the foundation, with sealed or overlapping seams. If doing this excavation, also a good time to put water barrier (bitumastic coating or equivalent) over the foundation to greatly reduce (unless you have high water table) the amount of moisture getting in under and potentially idffusing up through the slab.


This insulation "wall" will limit heat loss from the slab to the outside soil. Requires chemical treatment of all surfaces of the board or backfill soil treatment if in termite or carpenter ant country because they love tunnelling through foam board and will form nests in it as well as using it as a protected passageway to get to wood - so you need to provide a mortar or concrete backer board barrier at the top to stop egress from the top of the foam board to the house, and maintain a 6 to preferably 10" gap from household wood and siding - meaning the top of the board will almost always be 6 inches or more under ground. Top with clean gravel to act as insulation in that section unless completely plastered in epoxy cement mortar to prevent insect infiltration. Or use insecticide treated insulation for the outside perimeter layer - many manufacturers make an insecticide-treated insulation for foundations - the Dow product is called Blueguard as I recall, though I would still put insecticide spray on the board or insecticide powder in the backfill as a preventative - because you do NOT want a termite or carpenter ant colony taking up residence right at your foundation. In heavy termite country (where it normally does not get cold enough for the exterior insulation board to have much effect anyway) I would not use the exterior foam board - just too much risk of infestation.

Answered 2 years ago by LCD




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