Daylight basement insulation

[Andy Pratt]

Next summer I'll be moving and setting up my shop in the basement under my home in upstate NY and I'm trying to plan out how I'm going to insulate it.

The basement has a concrete slab floor, with quality cinder block walls up to the 8' height of the room, it's water tight and will be kept at around 60 degrees in the winter, with no conditioning in the summer. It is surrounded by earth on 3 sides (frost line is about 5', so around the basement floor if that matters), and has a normal door and a garage door on the downhill side. There's no risk of water coming in through the door due to the slope of the driveway

My basic idea is that I'll lay 2x4s face down on 16" centers on the floor, insulate between them with ridgid foam and put a hardwood floor over that. For the walls, I'll do the same (2X4s probably on edge, not flat though).

Is ridgid foam my smartest option for the walls, or should I just use regular fiberglass? I assume it's my only option for the floor.

Do I need a vapor barrier over the concrete on the floor? On the walls? Is it a better option to use one of the painted on barriers or lay down an actual sheet of something?

Thanks,
Andy

[Burt Alcantara]

My basement shop is similar to yours. I haven't done anything other then put industrial linoleum on the floor. The furnace is in an adjacent room. The previous owners installed ducting into the shop as it was used as a "family room" (whatever that is).

The result is too warm in winter and too cool in summer, but I don't complain. The other downside is it dries out wood very, very fast.

Perhaps, the main difference between our shops is I'm in a reclaimed desert area so it is very dry here. As I recall, the eastern seaboad can get pretty humid. Might make a difference.

Burt

[Chris Padilla]

I dunno about the floor...losing height might be a concern.

I think a vapor barrier is a good idea but use PT lumber when you secure the wood to the concrete.

Being surrounded by Earth, which is a darn good insulator, I'm not sure I'd worry too much about insulating the walls.

Do you have any time experience in this basement to judge by? Are you SURE you *need* to insulate?

Worse case, the wall not surrounded by Earth may need the most focus in terms of insulating....

[Andy Pratt]

I thought you couldn't use pressure treated lumber for anything indoors? I'm just vaguely remembering something a friend said about it off-gassing fumes or something, so I'm not sure.

I'm going to cover the walls no matter what for looks, ease of hanging things and so the shop room can be living space when I eventually move out of it to a real shop, so I think I should definitely insulate all of the walls, even the parts surrounded by earth, although you make a very good point about that.

I haven't spent time in the basement, but our winters get as low as 30 below, and my only major heat source is heat radiating from the woodstove upstairs, so I'll be lucky to keep it comfortable even with insulation (the hot air being hard to effectively move from upstairs down to the shop).

My other consideration: I'd like to do a solid hardwood floor, if I do the "floating" style, do I just let the 2X4s rest on the floor with no fasteners into the concrete? If I do a fixed floor with fasteners, is penetrating through the moisture barrier a concern?

Thanks,
Andy

[Chris Padilla]

Any time there could be a concrete/wood juntion, PT is highly recommended. As you know, concrete is porous and always lets water through it. That is why PT is recommended. Indoors should be fine, I think, but I'm not sure. Does PT off-gas?

As an experiment to see if you really want to use PT for the floor (and even walls), tape well a 1 square foot sheet of vizqueen (plastic) to the floor in various spots, wait 24 hours, observe. Dry as a bone? Wet? Soaked? A bit moist?

Whatever you do to the floors and walls, I'd try to minimize things such that you get max height and area as much as possible unless you determine that you need thicker insulation. Maybe you only need 2x4 ripped in half (furring strips) for the walls and floor?

Floor heaters might be something to invest in for your basement if getting the main house's warm air down there is difficult.

Solid hardwood floors always sound nice but they can be troublesome due to movement. Seriously consider an engineered floor...prefinished especially! There is nothing like slapping down a prefinished floor and being done. No sanding, no finishing. The finishes the manufacturers put on their prefinished floors are likely better than anything you do on site, too.

I believe the vapor barrier goes on the concrete first. Next are the sleepers (2x4s or whatever, nailed/glued), then you likely need a sub-floor on top of that (3/4" plywood?). Once you have that, follow the manuf. needs for whatever floor you choose.

[Jeff VandeZande]

I would be way wary of trapping moisture between the finished floor and the concrete and getting some kind of weirdo mold growing.
Even if you put a vapor barrier over the studs and styrofoam insulation
it would be difficult to seal out all of the moisture that would be attracted to the cooler floor.

[Tom Godley]

I have read about many and done a few basements.

I have used metal studs as well as wood studs for walls with both regular and foam board on the walls. If you have the space and the area is completely dry with no condensation problems you can do wood and regular insulation -- but if there is any condensation be careful.

You do not need much insulation for the walls.


I would recommend you use a product designed for basement floors - like a dry-core (sp?) type product - I have use it and it works well.

I have also installed 2x4s sideways and then framed a floor placing foam board between the 2x4s. I have only gone to this expense when I was installing radiant heat. You must use a vapor barrier and pressure treated 2x4.

[Steve Berberich]

I have an identical basement in Northern Kentucky and have researched a lot on this.

First, please review this site www.buildingscience.com for great insight on insulating basements. Second, it would be worth purchasing the book Weatherize and Insulation from Tauton Press. Highly informative. I've done both and am much more confident with my plan.

1. Seal all of the areas around the sill plate (see book for methods) and isulate the cavities.
2. Glue on extruded polystyrene (no vapor barrier) to the walls. Tape all the joints with contractors or Tyvek tape to seal from large vapor contact with the wall. Some foam board come tongue and groove and some come with indentations for firring strips. This applies, at least, to all the foundation walls exposed to the outside.
3. Either frame out a wall about an inch in front of the insulated wall or use firring strips on the foam. If framed, unfaced fiberglass can be used here. If framed, use ptl on the bottom plate.
4. For the floor, I will eventually be putting down the Dricore. Below I have copied an exerpt from a previous forum. This man had some excellent ideas to encourage air flow in his finished basement.

I am currently tuckpointing, removing paint and will soon be repainting the walls with Drylok to prepare for this. The hardest part has been removing the paint. See below for the above mentioned expert:

"I recently finished my basement and followed this approach:
1) Use a closed cell foam board insulation. I used 3" thick board, glued to the cement wall. This insulates the wall(is not a vapor barrier). Closed cell will not trap moisture but allow it to transfer thru, insulating the wall will help balance the temperature difference between in the conditioned air space and the basement wall. Its this temperature difference that will cause condensation and moisture to form.

2) I built a 2x4 wall, 1 inch away from the foam board. This wall was insulated with non-faced R13 insulation. The 1" void is important, if moisture does migrate thru the foam board(it will) you want a channel for it to escape and not get trapped in the insulation. Yes this uses more floor space, but I am willing to give up a few inches of floor space to be sure I don't have a mold/moisture issues down the line.

3) I also used a flooring system call DriCore. I sealed my basement floor with DriLok, then laid the DriCore over it. I made sure the ventilation channel under the floor connected to the void in the wall. I installed floor vents(4"x8") thru the DriCore in several places in the basement and connected one vent to the cold air return on my HVAC system to draw air thru the system.

I also used pressure treated wood for the sill and galvanized steel studs. I figure the less 'food; I provide for mold the better. The steel studs were a breeze to work with and the walls came out perfectly straight.

Its been 5 years since this was done and so far the basement is very dry and feels fresh - no humidity feel that many basements can get.

I live in Northern Ohio, so winters are cold and summers are humid. My basement never had a water problem, but before it was finished it had a humidity problem. My dehumidifier ran constantly, filling its 2 gallon tank up every day, now it takes about three/four days for it to fill up the tank.

Hope this helps."

[Joe Chritz]

Pressure treated lumber is fine as long as you don't burn it and then eat the ashes. Yes it can leach chemicals but the amount involved and time needed are so that it makes it basically a non issue.

There have been many tests on soils involving building planter boxes from PT lumber.

You likely only need a minor break for the walls surrounded by ground. 2x4's on the flat with 1.5" styrofoam should be fine if you insulate it at all.

A vapor barrier is a good idea.

Joe

[Prashun Patel]

Round me, pt is required for lumber contacting the foundation.

I used dri-core in my basement bathroom. Great stuff. But if yr putting 400-500lb stuff on it like a tsaw, why bother? You won't get much warmth from it. Yr better off with industrial linoleum. Far less upkeep. Anything with seams like a strip floor is going to be a nightmare with dust.

Definitely insulate the walls. That will make a HUGE difference in comfort

[Matthew Voss]

I would skip the 2x4s on the floor all together.

1" rigid foam (EPS) on the floor with exp foam and seam tape and 2 layers of 1/2" plywood directly over the foam.

The foam has the compressive strength to support the 2-layer plywood subfloor without the sleepers.

NEVER use a vapor barrior in a basement.

[Andy Pratt]

Steve - Thanks for all of the excellent info, those were great articles and that website is a great resource, very professionally written stuff.

It seems like the vapor barrier trend is the big problem, causing condensation in the walls and rotting wood. Does not putting up a vapor barrier have a serious detrimental effect on the woodworking environment? I think a lot of people complain about humidity issues if I remember correctly. Maybe I just have to run a dehumidifier, as it seems like the construction methods you mentioned are the only acceptable ones.

The articles mention furring strips on top of the expanded polystyrene, is it important to leave the air gap these create, or can that gap also be filled with ridgid insulation? This relates to the last post, as it would be doing approximately the same thing (moisture wise) as placing the gypsum board/plywood right over the foam.

Finally, on the flooring side: do I need to put gypsum board down over the foam (as it needs it on the walls for fire rating) or does that not apply to the floor?

Thanks,
Andy

[Chris Padilla]

Drywall on the floor? Uh, no, I don't think so.

[Matthew Voss]

This relates to the last post, as it would be doing approximately the same thing (moisture wise) as placing the gypsum board/plywood right over the foam.

Finally, on the flooring side: do I need to put gypsum board down over the foam (as it needs it on the walls for fire rating) or does that not apply to the floor?

Thanks,
Andy

The dew point temp is somewhere inside the foam, so the face of the foam is warmer and not subject to condensation.

And, you need an acceptable subfloor.

[Matthew Voss]

The articles mention furring strips on top of the expanded polystyrene...

I prefer a stud wall over furring strips - this allows the depth for easy installation of the elec. boxes.

Also, I don't think I've ever seen concrete basement walls as plumb or straight as you could build the stud wall.