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posted: 7/20/2014 12:01 AM

Aim to keep frost at bay when insulating basement walls

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Q. I have a concrete block foundation that ranges from fully exposed to totally below grade. The basement area is dry, and I intend to finish the space. What method of insulation would you recommend for the walls, and would you recommend a vapor barrier?

A. The fully exposed foundation can be insulated from the floor to the ceiling with 1- to 2-inch thick XPS (extruded polystyrene) adhered to a clean surface with polyurethane caulking or Styrobond.

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The below-ground foundation is another story. To be safe, you need to be sure that there is a functioning foundation drainage system in a stone bed protected from backfill contamination by a filter fabric and that the backfill itself is made of mostly coarse material. You also have to make sure the grade falls away from the foundation. Unless these measures are in place, insulating foundation walls more than three feet below grade may entail some risk of frost pressure cracking the walls. This has even happened to poured concrete walls.

As the insulation reduces heat loss through the foundation, frost will penetrate more deeply.

By only insulating to three feet below grade, the heat loss below the insulation is enough to hold the frost in check before it can cause serious damage. At least, that has been the thinking in the building science field for many years.

An alternative is to excavate an area a minimum of 1-foot deep against the foundation and slightly deeper as the excavation extends to 4-feet away. Make sure the ground is smooth and lay 2-inch thick XPS on it. Backfill and grow grass or a thick ground cover. Frost will be stopped by the insulation and the ground below it will remain frost-free.

With the use of XPS on the inside walls, and with joints taped, there is no need for a vapor retarder. Build the stud walls in front of the XPS and finish them with paneling or drywall. For the above-grade walls, you may wish to put in fiberglass between the studs for additional insulation.

Q. We have a 10-year-old log home in the Upper Peninsula of Michigan. In the past, I have used high-quality deck stain on the logs. The stain, however, does not seem to last, especially on the south- and west-facing sides. Do you have a recommendation on what the best log stain would be?

A. How long does the stain last? Any stain subjected to the sun will need to be reapplied every two to three years. It's best to choose a brand containing UV protection, but even with any of these, regular reapplication is essential.

Q. I have a small cabin with a heated live-in basement in southern Vermont. The cabin sits on a hillside with an approximately 3½-feet above-grade block foundation on the downhill side tapering to zero on the uphill side. There is roughly 150 square feet of exposed block foundation, not including windows. I am looking for suggestions for insulating the above-grade exterior basement walls. Because of built-in cabinets and bench seating, interior insulation isn't a very practical option. Can you recommend an exterior foundation insulation system that would be relatively weed whacker-proof, have a reasonable R-value, as well as won't turn into a carpenter ant highway?

A. Probably the best way to insulate your foundation is to clean the blocks and adhere 1-inch thick XPS rigid insulation to them with Styrobond or a polyurethane caulking.

Cover the insulation with half-inch pressure-treated plywood, which will need to be fastened to the block walls by means of power shots. It will also need to be properly flashed to the siding.

To keep carpenter ants at bay, you will have to treat the base of this new construction with an ant spray yearly in the spring, or have the ground treated with borates by a pest-control firm.

Q. I am replacing my home's cedar siding with Hardie plank, and will also add insulation. The house has 2 inches of mineral wool insulation in the walls. Would it be better to have cellulose added to the wall cavity or 1-inch foam to the outside?

A. Blowing cellulose into the wall cavities will crush the mineral wool. Hardly worthwhile. It is best to add 1-inch XPS or polyiso over the existing sheathing.

You should seriously consider covering the rigid insulation with Benjamin Obdyke Home Slicker Plus Typar to obtain a rain screen/breathing space. This will be very helpful in keeping any siding in better shape.

Q. I think I read a column you wrote about Hardie board not being what they say it is cracked up to be. Can you give me more information about this? We have a cedar house and it really needs painting because it is exposed to so much sun. It is very expensive to paint every few years, and we thought we would change it to Hardie board, or do you have any other suggestions?

A. Hardie board will need to be painted on all sides before installation and requires periodic maintenance, so you are not gaining much over time.

By the time you remove the cedar siding and dispose of it, prepare the Hardie board and have it installed, you will have spent more than the cost of keeping your cedar house in good shape.

The problems I was referring to were caused by Hardie changing its installation instructions every few years as it became aware of failures. That does not instill confidence for me.

Q. I repeat the praises of many for your sharing your knowledge in the Daily Herald.

Some years ago, I had insulation blown into our roof space. At the time, the technician suggested having two wind turbines installed, which I subsequently had done. His point was that turbines would remove moisture and heat in summer and moisture in winter. Can I assume this has been the advantage we've been having?

A. Wind turbines are not very effective. It would take more than two to accomplish much cooling and moisture removal in an average attic.

But if you have not experienced any problems, however low their level of effectiveness, they are doing something for you.

The best way to ventilate an attic is with a combination of full-length soffit vents installed a few inches away from the house walls and a full-length, externally baffled ridge vent similar to Shinglevent II. There must be an uninterrupted air space between the soffit and the ridge vents.

Q. About seven years ago we hired an experienced painter to stain our shiplap-sided house. We chose Cabot stain for the siding and Cabot finish for the trim in the same color. We have a breezeway sided with the same shiplap connecting the house to the garage. It became apparent after a time that the painter had dipped his brush in both types of material when painting the walls of the breezeway. The result is that one wall was painted with the area covered with Cabot finish and is still tacky to this day. On another wall, brush strokes show where both finishes were applied side by side. Also, there is considerable mold or mildew. I want to stain or paint the breezeway and don't know how to proceed so that all areas accept a new finish.

On another subject: Five years ago we replaced our old, inefficient oil burner with a Freedom 2000. It is more efficient, but is noisy and has already needed a new circulator pump and a temperature sensor. I guess the saying that "they don't make things the way they used to" applies. My Hotpoint refrigerator, microwave oven and dishwasher that were installed when the house was built 35 years ago are all in perfect working order.

A. It doesn't sound to me as if the painter was experienced.

Where the coating is still tacky after seven years, you should remove it and start anew. A paint and varnish remover should be used. You may want to try that also to remove the brush strokes.

If the products you used contain linseed oil, mold and mildew will thrive on them, unless a mildewcide had been added. Mildew can easily be removed with a detergent solution.

To kill mold, you'll need to use a solution that will kill its roots as well as the surface manifestations.

There are a number of ways to kill mold. You can use white vinegar, borax, boric acid, tea tree oil (expensive) and grapefruit seed extract. All these are safe ecologically, but some have odors.

You can buy grapefruit seed extract in health food stores. Mix 10 drops of the extract per cup of water in a spray bottle. Shake it up well and spray it onto the surface to be treated. Leave it on; there is no need to wipe it off unless it is necessary to wipe off the dead mold spores. If you do so, spray again and do not rinse or wipe off.

Both tea tree oil and grapefruit seed extracts can be saved in the spray bottle; they remain effective and stable for a long time.

If you are asking how to mitigate the noisier furnace, I would need to know a lot more. I assume it is in a basement, but is it in an area that can be somewhat isolated? Is the ceiling open to the floor joists or finished?

Q. I have a 45-year-old garage floor that is showing lots of damage due to road salt and slush drying on the floor during the winter. Also during the winter are areas of efflorescence. But in areas where old motor oil has been spilled and wiped-up, the floor is in good shape. Would it by worth a try to apply motor oil to the floor and let it soak in and then wipe the excess?

I am not concerned with appearance, but just would like to preserve the floor for a while longer.

A. There are commercial preparations based on mineral spirits and boiled linseed oil, but they do not dry effectively when applied to indoor surfaces.

Since your garage floor is not in the best shape, you have nothing to lose in trying what seems to have worked for you.

Efflorescence is the remaining salts in most masonry products after the water content, which caused the salts to melt, has evaporated. In your case, it means that moisture from the subsurface has diluted the salts and brought them to the surface. Efflorescence can easily be wiped or brushed off.

• Henri de Marne was a remodeling contractor in Washington, D.C., for many years, and is now a consultant. Write to him in care of the Daily Herald, P.O. Box 280, Arlington Heights, IL 60006, or via email at henridemarne@gmavt.net.

© 2014, United Feature Syndicate Inc.

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