Submitted by Ad-Nauseam91 t3_z82h4d in DIY
more_than_just_ok t1_iyaky3n wrote
Reply to comment by strongmans in Plan to frame part of basement and have a few questions by Ad-Nauseam91
This is correct method. Foamboard directly on the concrete leaves no room for convection. In winter the top of the basement wall will be cold and the bottom buried part will be warmer. You do not want warm air moving and coming into contact with the cold and condensing the water out. In an unfinished basement this isn't a problem because enough heat is being lost through the wall that the dew point is somewhere in the wall, but once you insulate inside, the inside of the concrete will become colder.
u/strongmans suggestion to frame a proper 2x4 wall, not just use furring strips, is also a good one, because then you have a proper wall to hang stuff on in your shop and you have room for electrical boxes on the exterior walls.
Ad-Nauseam91 OP t1_iyav3nv wrote
Thank you and u/strongmans follow up question around the different temps in foundation higher up than lower. If I were to frame, insulate and drywall the walls, but leave the floor as is, that doesn’t create any weird effect? What if I leave the ceiling as is too (not sure I’d do that but curious if that changes anything)
ComDet t1_iyb1ajv wrote
I would also recommend doing epoxy floor, and treated wood at least for the bottom plate.
more_than_just_ok t1_iyb4qhw wrote
Epoxy floor would look nice. I said I would do it on my floor 10 years ago, but it hasn't happened yet. You can do treated wood for the bottom plate in each wall, the other option, u/strongmans mentioned it, is sill gasket, basically 3.5 inch wide closed-cell foam, about 1/8" thick that comes in a roll that you put between the bottom plate and the floor. It's also used between the top of the foundation and the sill plate (or anywhere wood touches concrete) in most newer houses.
If you're building just a few walls yourself, spend the extra money and use 2.5 or 3 inch deck screws instead of nails (Robertson #2 head if you can get them in New England?) Very useful when you mess up and need to redo stuff, and you can hold the board with one hand, the drill in the other while the drill bit holds the screw in place.
nightwing2000 t1_iybav2m wrote
I thought Robertson (the square hole screw heads) was more of a Canada thing?
Yes, my go to reference for construction, Holmes on Homes, says NEVER have bare untreated wood touching cement. It can absorb water from the cement.
You also have to consider the risk of basement leakage. Cracked foundation wall leaking, or rain/melt water buildup leaking in, may damage the bottom of your walls. Is this a risk? How good is the foundation drainage? Would you notice?
And, in much older houses, the concrete basement floor may not be particularly level. A raised wood subfloor allows you to level things so you can use tiles or carpet. But you may have a central floor drain, you may never notice if there's a water seepage until mold shows up, etc. Basement floods do more damage if you have to replace a raised floor. (I saw a Holmes episode where he used a floor leveler compound, like a very wet cement that leveled like water but hardened - to get rid of excessive slope. Don't block the drain. )
Mego1989 t1_iyblhsf wrote
Self leveling underlayment/cement. It's neat stuff! Very messy and expensive though
Doctor_Frasier_Crane t1_iycmpz5 wrote
I used 12-inch wide 6-mil poly under my basement walls and wrapped it up both sides and stapled it in place. Provides separation from the floor and some minor flood protection. I can get up to 6 inches of water on the floor and still have some protection for the studs.
I also have rolled dimple flooring underlay to provide separation and airflow under the vinyl plank flooring.
Dire88 t1_iybaqxg wrote
Technically, you can skip PT on the bottom and sill plates if using sill guard. But the cost savings for non-PT aren't worth it imo.
strongmans t1_iychzmi wrote
You'll be fine. It's when you close in the walls preventing air movement is why you need a vapor barrier. I've done this method tons of times and never an issue. If it's going to be a shop why bother finishing the floor. Unless you want to spend the money and epoxy it for looks.
You can use PT for the sill plate if you want but it's going way overboard. The sill gaskets breaks the capillary movement of moisture. You shouldn't use PT lumber inside but it's not the end of the world.
more_than_just_ok t1_iyb2s8v wrote
You can leave the floor as is, especially for a workshop, and leave the ceiling unfinished too. My basement is 70% fully finished (drywall ceiling, carpet) but I've left the laundry/utility room and a storage room with no ceiling and a concrete floor.
JohnC53 t1_iybynw2 wrote
All the exposed joist space makes for a ton of additional storage if you get creative. Another bonus of leaving the ceiling unfinished.
nightwing2000 t1_iyb8cyc wrote
Exactly - why would you want air movement behind the interior walls? All it does is guarantee that if there's one cold spot, instead it makes the whole area behind the insulation a cold spot. Especially the ground level cold will migrate to the basement floor level, spreading the love. Insulation flat against the walls makes sure any cold does not spread beyond where it's cold through the wall.
In Canada, where winters are probably colder at times, the standard now is 2x6 exterior. Or... for basements, a sheet of styrofoam insulation, then insulated 2x4. If you plan to put weight on the walls as others mention, with cupboards, shelving, or tool pegboards- you want the strength of 2x4 on standard 16-inch centers.
The vapour barrier should be on the hot side of the insulation, so inside humidity in winter does not migrate inside the walls to condense. Usually for pink fiberglas insulation, this is plastic sheet on top of the wall, stapled to the studs. Typically, it's "glued" using acoustic sealant so the holes from the stapes are sealed. Electrical outlets 9and cable TV, network, etc.) are on the warm side of the plastic, using tape to seal the wire coming through the plastic. the key is NO AIRHOLES.
(Alternative construction is sprayed in expanding foam, which is then sawed flat level with the studs when it hardens. Since it's sprayed as a liquid and forms a continuous piece, a vapor barrier is unnecessary, it's already airtight.)
Take pictures as you do the work, especially of the walls before sealed from view. Not sure where you are, but here you can do electrical yourself if (a) you know what you are doing and (b) with the supervision of a qualified electrician. (I.e. he/she says "yes, that's up to code".)
Some municipalities require a building permit, especially if you touch electrical or plumbing. I has a relative in the USA, when she sold her house 20 years later, someone somewhere went through the house's building permit history (house inspector?) and claimed the family room behind the garage was never issued a permit to be finished. AFAIK she bought it finished. Then bought and remortgaged when she bought the half it from her (ex)husband, with no hassles. I sold my house in Canada with no such hassles. How persnickety is your municipality?
Dire88 t1_iybbshw wrote
I had to demo 36ft of basement wall due to a water damage issue, and was set on doing it properly with 2in XPS while maintaining the existing wall thickness due to existing clearances.
Ended up going with 2x3 studs mounted flat on the XPS foam. To account for deflection if loads are added to the wall, I slapped two 5in tapcons through each stud.
Run electric through the joists and down between studs. Can add additional 1in insulation if desired.
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