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Basement finishing advice

Posted by rsteventon (My Page) on
Tue, Aug 19, 08 at 15:39

Hi All,

I 'need' to finish my New England basement due to a new 'addition' coming soon. The basement is pretty dry. There was not even a sump pump installed until I put one in (although there was a sump pump hole!).

I will be doing about 60% of the basement. Leaving the machinery room and laundry unfinished.

After finding this forum, I have read back and tried to learn as much as possible. I am going to propose my current thinking, and would like some feedback.

Sealing:
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Thoroseal on the walls (I read that Drylok is crappy).
Not sure about 'sealing' the floor. Some people say that it may crack the floor due to hydrostatic pressure, but I doubt that!

Floor:
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I want to use a Pergo type 'wood' floor.

I am not sure if I should put down:
- foam + ply (Homes on Homes method)
- Dricore (if it gets wet, you are screwed)
- ThermalDry
- Delta-FL (apparently, it 'creaks')

Framing:
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Pressure treated wood on the bottom. Tapcon screws into the floor. Why not use pressure treated wood for the rest of the frames ?

Do I floor to the edges of the walls, and mount the frame on top, or frame and then lay the floor to the edges of the frame and caulk ? Is the answer different eg: for foam vs. Delta-FL ?

Insulation:
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The walls are high pressure concrete. I have tried and failed to drill into them. Therefore fixing XPS to them is kinda out.

I plan on using fibreglass/etc in-between the frames and putting a membrane in there too (remember, I already have Thoroseal on the walls, but I am concerned about damp air from the un-finished side of the basement).

Drywall:
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I saw you can get 'mold resistant' drywall sheets for extra cost. Is it worth it ?

Other notes:
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I plan on using recessed access panels built into the drywall for access to valves/etc.
Ceiling will be drywall or dropped. I have not decided.
In-law is a certified electrician.
Downlighting.
I don't have a humidifier on the furnace.
The house has central air. I plan on connecting it to the open plan room (well, paying someone at the framing stage).
Once done: slam a hygrometer down there and keep it below 40-50% using a dehumidifier.

Thoughts ?

-Richard


Follow-Up Postings:

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RE: Basement finishing advice

Framing: Instead of pressure treated, slit strips of 1/2" XPS and put it underneath. No need for pt anywhere. If you insist on using it, cut it outside with a mask, not inside your home.

If you bother with any interior foundation coating, use crystalline type. Not only does it work better than cementitious coatings--it's used for swimming pools, pollution control tanks etc.--it goes deep into the concrete structure and will bridge small cracks should they appear later.

The walls are high pressure concrete. I have tried and failed to drill into them. Therefore fixing XPS to them is kinda out.

Get a better drill! Or rent one. I used to drill 30mpa foundations all the time. Now, I've switched to closed cell sprayed xps foam.

Since your labour is "free", go for the XPS (or EPS) followed by fibeglass. Forget the vapour barrier! If you still insist on the fibreglass--"hey the guy at the lumberyard told me this is what everybody uses"--look for Membrain, a vapour barrier that changes the flow of vapour depending on the weather.

If the mould resistant drywall is the same price, sure. Otherwise, save your money. If you get serious moisture problems, the resistant drywall won't last long anyway. Just be sure to keep your dehumidifier on!

I never use wood for basement floors. But the foam system has been recommended by Building Science. Though your concrete floor is missing some of their other recommendations.

Of course, laminate is not wood, but a picture of wood laminated onto a substrate. If you use it, be sure to buy one that is approved for basement use.


Here is a link that might be useful: Basement Insulation Systems


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RE: Basement finishing advice

Worthy gives great advice.

Our basement was finished before I ever saw his posts but, fortunately, is done much like he receommends. I did use PT for the floor sill plate. Because our foundation is exterior spray coated with a rubberized sealer, the basement is very dry though I do have a cold air return to circulate air and condition the space.

The best advice I can add is to make a plan to scale - even mark some locations on the floor with tape to "live the space" before commiting to lighting, plumbing and heating placement. Good luck.

Here is a link to ours.

Here is a link that might be useful: Our Basement


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RE: Basement finishing advice

Thanks for the vote of confidence!

Returning the compliment, your basement looks bright, livable and lived in.

I should add some reasoning to my first post. Wood, pt or not, directly on the floor will be subject to moisture rising through the concrete. I've seen pt fence posts significantly rotted at grade in as little as 15 years. I used to put 6 mil poly under the plates--it's actually manufactured in rolls for that. But the Building Science recommendation of xps isolates the wood better and lifts it above the inevitable floods. And floods are why I just don't like wood floors in basements. No matter what you do, unwanted water always seems to end up in the basement. In my case, it's come from overflowing eaves during unusual downpours, inadvertently stoppered-up 1st floor laundry tubs, a burst connection from an overtightened fitting and my kids opening an outside faucet in winter that come the thaw created a nice backyard pond. When you have carpet (no padding!) tile or stone, it's just a matter of grabbing a mop or wet vac.


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RE: Basement finishing advice

Thanks for all the feedback.

My understanding is that I should:
- use a crystalline internal foundation coating. However, I cannot find any product names, but links online indicate that the surface needs to be roughened to ensure open cells for proper diffusion into the concrete. This requires sand blasting or shot blasting or acid etching. Comments ?
- How about gluing the XPS foam to the wall ? It's a chemical bond instead of a mechanical fastner, but if it gives way, then you probably have WAY too much water pressure on the inside of you wall !
- XPS on the floor, with caulking on the sides against the walls.
- Fiberglass sheets ? (you were not specific) on top of the XPS as a subfloor.
- PS lumber on the bottom of the frame ON TOP OF the subfloor (tapcon'd into the concrete floor below ? ... do I silicone each hole before adding the bolt ?)
- use basement approved floor
- upgrade my 'toy' drill :)


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RE: Basement finishing advice

If I felt there was a strong possibility that the wall would leak, I would apply an internal coating. If your walls are externally waterproofed with plastic membrane, flexible applied material or built up membranes or are dry even in pouring rain, I'm not sure I would bother, as this is not a cheap product.

When I used crystalline waterproofing, it was externally on new construction before plastic membranes were available. I used Permaquik, since acquired by Tremco. Prep included washing down the wall with a solution of muriatic acid. This is quite corrosive and required heavy duty long rubber gloves and full face masks. Newer products may require different prep and application methods. Names I see frequently are XYEX and Kryton Intl.

The fiberglass is for the walls in addition to the XPS or EPS. (I only suggest it because it is usually cheaper than the foam boards.)

Glue on poured hasn't worked for me; poured walls are too irregular.

Tongue and groove XPS makes a tighter fit. If you don't use t&g, use building tape (the red stuff) on the seams

PS lumber on the bottom of the frame ON TOP OF the subfloor (tapcon'd into the concrete floor below ? ... do I silicone each hole before adding the bolt ?)

That'll work. Silicone not needed.

upgrade my 'toy' drill :)

A good quality 1/2" hammer drill. I've used fender washers. But I've seen other installations using long 1x2s perpendicular to the foam boards.

It wasn't mentioned. But be sure to insulate along the rim at the top of the wall and between the joists. On new construction, I have it sprayed.

Good luck!


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RE: Basement finishing advice

Rich,
you have receive some good advice. I would like to emphasize that you include some sort of supplement heating source in your plans. Especially with a new baby on the way, you want a warm and comfortable basement in the winter.
Tapping into your existing central heating system may not adequately warm the space. Some people find this out when its too late.
Enjoy your new basement and baby!
-jasper


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RE: Basement finishing advice

Hi guys,

Thanks for all the excellent advice so far ! This brings up a few more questions.

The basement is pretty dry. The only time it has flooded was a few months after we moved in (go figure). The flood stage on the local river is 9ft. It sat at 15 ft for two solid weeks. We had a sump pump hole with no sump pump in it. Water came up out of the sump pump hole to a level of 1/8 inch across half the basement. There is now a sump pump.

What are the reasons for going with XPS on the walls vs the traditional fibreglass stuffed between framing ? I assume it is to reduce the air in contact with the (colder) wall and hence reduce condensation ? This would imply that you really want a good fit between the two.

So, how many fasteners to hold down the XPS sheet and in what configuration ? 4 Corners + 1 in the middle ? OR do I go medieval on the thing and use a fender washer every one or two feet ?

RE central heating: I will get the existing system extended. The finished part of the basement is going to form a single L shaped room with computer in one side and gym on the other. The house is only 1300 sq ft, and the half basement will be another 400 sq ft. Yes, it is significantly increasing the size of the heated area. However, I think the furnace is rated for a large air volume, so I will check the output etc.

RE Insulation at the top of the walls. There is currently fiberglass with paper backing at the top. Could I just leave it there, or should I rip it out and use a spray foam product ?

-Richard


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RE: Basement finishing advice

Jasper's advice about heating is an important thing to consider. Yes, have your furnace ducting incorporated into the basement and by all means have cold air returns installed.

Our basement is comfortable when the house is calling for heat (or cooling) in the winter or summer. However in the spring/fall it can be cool. We intalled an electric fireplace for auxulary heat during those times.


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RE: Basement finishing advice

What are the reasons for going with XPS on the walls vs the traditional fibreglass stuffed between framing ?

In a cold climates, in the summer, XPS allows drying to the interior of the wall above and below grade without being affected by moisture. During the winter, it prevents any significant amount of moisture laden air from reaching the foundation wall and condensing on it and causing mould problems. At the same time, it provides a much higher effective R factor than fibrous materials because it is continuous and resistant to air currents.

There is currently fiberglass with paper backing at the top.

Remove it, as it will eventually get moisture laden; besides it does a poor job of insulating. You have several choices for this area, depending on your budget and plans. It can be professionally sprayed with either open cell (oc) or closed cell (cc) foam (I prefer cc.) There are some DIY alternatives that some users seem well satisfied with. Or you can use pieces of XPS, EPS or isocyanurate board tightly fitted between the joists. Finish up with handheld sprays and caulking for any gaps.

Fastening the foam board: Whatever works to hold the board tight against the wall. Last time, I used about five-seven per board. My helper figured out a way to hold two adjacent boards with one washer by putting the fasteners near the edge. You might also see if you can find non-metal fender washers, so you're conveying less cold from the basement wall to the warm side.

Here is a link that might be useful: basement insulation systems


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RE: Basement finishing advice

I've been researching this of late for my own project. I'll describe what seems to be the best practices.

Use 1" to 2" XPS on the floors. Use tongue and groove or shiplapped sheets and tape all joints. Leave a 1/4" gap at the walls and fill with expanding foam. Cover with 1/2", 5/8", or 2 sheets of 1/2" plywood tapconned through the XPS to the floor. I'm not convinced DriCore or Delta-FL are better products as they do not create an air barrier at the floor to prevent condensation and the ensuing mold and mildew. They try to mitigate this by telling you to install floor vents and to keep the humidity low with a dehumidifier.

For the rim joists, tightly fit XPS in the cavity and caulk, foam, or tape into place to create an air barrier. Fill the rest of the cavity with batt insulation.

For the walls, glue 1" to 2" XPS to the walls wrapping the top of the masonry wall. Foam any gaps, tape all seams and the top and bottoms thoroughly to prevent any air from getting behing the panels. Frame your wall against the XPS. Nail top plate to the joists and tapcon or shoot the sill plate to your insulated floor. No pressure treated wood is required since only XPS should be touching the masonry. Set your studs 16" on center between the plates. Install electric and plumbing. Fill between studs with unfaced batts if appropriate for your climate. Batts may not be necessary if 2" XPS is used on walls. Sheetrock the wall with a 1/2" gap between bottom of sheetrock and floor. I would use mold resistant sheetrock, this is exactly the type of situation that it is designed for.

I wouldn't waterproof the walls. Moisture needs to migrate inward from the concrete, especially if you have an exterior waterproofing already. Moisture wicked up from the footers or other areas needs to go somewhere. Water vapor will migrate through the XPS, unfaced insulation, and sheetrock as it should. Problems occur when you trap moisture into the concrete wall with waterproofing or you trap moisture into your finished wall with vapor barriers.


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RE: Basement finishing advice

Hmm.. Interesting about Dricore/etc wanting low humidity. I had assumed that if the floor was clean and any water did migrate up through it, it would be trapped between the floor and the plastic backing of the Dricore and the resulting mold would have nothing to eat/live on.

I was planning on sealing the walls with Drylok. Not sure what to do with the floor. Does anyone have any suggestions ?


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RE: Basement finishing advice

Problems occur when you trap moisture into the concrete wall with waterproofing or you trap moisture into your finished wall with vapor barriers.

Exactly. That's why I recommended crystalline waterproofing on the interior, as it protects against hydrostatic pressure while permitting the flow of air and vapour. (See Link.)

Whether or not crystallline waterproofing is needed in your case is up to you to decide. The only water mentioned entering came up through an unused sump pit.

Here is a link that might be useful: Xyprex waterproofing


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RE: Basement finishing advice

Ohh.. coolio! Now how the heck can I get that stuff in the USA ? Even the manufacturers website does not list availability in the USA


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RE: Basement finishing advice

"Hmm.. Interesting about Dricore/etc wanting low humidity. I had assumed that if the floor was clean and any water did migrate up through it, it would be trapped between the floor and the plastic backing of the Dricore and the resulting mold would have nothing to eat/live on."

If it's clean... Mold will grow on any dirt or dust that collects under there if stays damp. If you install with the proper venting, how clean is it going to be after a few years? Just my point of view. I'm not an expert. DriCore is a pretty expensive product and goes against the modern practice of creating an air barrier against the masonry surfaces to prevent condensation.


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