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posted: 2/17/2013 4:00 AM

New driveway needs proper stone base

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Q. This spring, I plan on making my driveway bigger to accommodate my new garage. I need to excavate some topsoil and put a base under it. My question is: Should I use No. 4 stone, No. 3 stone, 2-a modified or 2-b stone, or a combination of all? I plan to let it sit about two full seasons before I pour concrete to allow for any settling. Is this enough time to allow for that?

I thought about 6 inches of No. 4, 6 inches of No. 3, 6 inches of 2-a modified, then choke the rest out with 2-b No. 67 stone.

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When I do pour concrete, should I put it in at 6 inches or 8 inches thick? My neighbor did his at 8 inches; is that overkill? He has no heavy traffic on it; however, I will have to bring a truck up my driveway to pump my septic tank occasionally.

Also, I plan on heating my driveway. What methods are available for this, and which is the best? What PSI (pounds per square inch) rating should I use? What about fiber reinforced versus wire? Any suggestions or ideas will be greatly appreciated!

A. When the substrate is properly prepared, there is no need to wait for settlement. If your soil is clay or silt, you should consider excavating 2 to 3 feet of soil. You may also want to put geotextile fabric on the ground to prevent the stones from settling if the ground is subject to movement if it gets wet. Fill the excavation with -inch minimum to 1-inch fractured stones, leaving space for a 6-inch concrete pour. If you decide to heat the driveway (more on that later), the recommendation is to place 3-inch-thick XPS (extruded polystyrene) on top of the compacted stone bed, so adjust the depth of the stone bed accordingly.

If your soil is sandy, excavate down only 16 inches; there is no need to lay fabric. Spread 10 inches of grade 8 fractured stone (-inch). In either case, compact the stones with a mechanical tamper.

The best practice for a trouble-free driveway is to install No. 4 steel re-rods 16 inches on center, set 2 inches off the stones with plastic "seats," and pour a 6-inch-thick, 3,500 to 4,000 psi slab. The slab will need to be scored to prevent cracking in erratic patterns, and it should be sealed, preferably with a penetrating sealer, which is permanent. Topical sealers need to be reapplied yearly.

To ensure proper placement and curing of the concrete to avoid dusting, spalling, etc., it is most important to select a contractor with extensive experience. Your local contractors may find the general guidelines I've provided "over the top," but experience with lesser measures has sometimes resulted in expensive failures in cold weather areas.

Since you intend to heat the driveway, a very costly and energy-consuming practice, you need to lay the XPS on top of the stone to prevent heat loss to the ground.

If you have a boiler with a hydronic central heating system, have an HVAC contractor check to see if it has enough capacity and can be zoned to heat the driveway. The fluid in the system will have to have antifreeze, which will reduce the efficiency of the entire system.

If you have a warm air central heating system, ask your HVAC contractor what he or she would suggest, such as an independent water heater solely for the driveway or an electric mat system. In that case, a licensed electrician is the person for the job.

Q. Our house is 40 years old, with two-by-four walls and 2-by-12 ceiling rafters. All the second-floor ceilings are cathedral. All are insulated with fiberglass and a vapor barrier, and proper vents were installed. Per the photos, the roof is comprised of two shed roofs. I have two concerns:

• Increasing the R-value in the whole house.

• Most immediate, solving the heat loss/ice buildup on the north-facing roof. It gets little sun and there is a lot of heat loss that causes melting. The three skylights, three vents, crawl spaces over bathrooms and stairwell all show heat loss after a light snow as those places go bare first.

In theory, the roof was built as a cold roof as it has soffit vents at the bottom and top and proper vents along the span. However, the cold roof is not working for all the reasons mentioned, along with probable settling of insulation, incorrect proper vent installation as they are often crushed when insulation is installed, etc.

The question is: Would blowing in insulation between the rafters, while giving us a much greater R-value, still leave us with a warm roof because we removed any cold air flow we now have with the soffit and proper vents and lead to continued, though maybe less, melting and freezing of ice? If a new roof is involved, then of course the roofing material is a question: shingles or metal? I would think metal would allow the snow to slide off readily, particularly if the skylights were removed as barriers, but as it is a pretty long span, I worry about little avalanches sliding off and burying kids and pets. I will be interested to hear any thoughts you have.

A. Your question involves only the roofs, so we won't discuss your desire to improve the energy efficiency of the walls.

Fiberglass, even with a properly installed vapor retarder and ventilation above it, is not the best insulation to use in a cathedral ceiling; closed-cell polyurethane is more effective. Some roofs with that type of foam sprayed to fill the rafter cavities function well as hot roofs, but it is rough on the shingles because they get very hot in the summer when the sun shines on them. Some shingle manufacturers cancel the warranty in such cases, but shingle warranties are difficult to collect and nearly worthless.

Some off-the-shelf foam baffles are flimsy and easily crushed by fiberglass, which, by the way, is unlikely to settle, but more likely to expand. The result is that you really do not have a cold roof, as there is little, if any, effective ventilation. I also do not see any evidence of ridge venting on your photos, in spite of your mentioning that soffit vents were installed at the top; there are no soffits at the top of your two roofs.

It would make no sense to blow in cellulose; it would crush the fiberglass and possibly make matters worse.

You have several options. Since the house is 40 years old, you must have installed a second roof, which may be close to the end of its life. This is probably the best option: Remove the existing shingles. Have a few sheets of plywood removed, most from the top of the roof, to see what is going on with the baffles and the insulation, and check the condition of the plywood, which may show signs of deterioration from years of possible condensation.

If all is well, and if the baffles are pretty much crushed, put the plywood back if it is in good shape, and cover the entire roof with 2-inch-thick rigid XPS (extruded polystyrene) foam. Screw 2-inch by 3-inch strapping vertically 16 inches on center through the foam and onto the existing rafters. Let the tails of the strapping hang beyond the existing fascia by 3 inches in order to install an off-the-shelf continuous venting strip on their bottom. Install new plywood, an ice and water protective membrane on the bottom 3 feet and a new fascia.

Shingles would be less expensive than a standing seam metal roof, but they would not last as long. Snow guards can prevent snow from sliding off the roof.

At the top of the taller roof, install Air Vent's Peak FilterVent, an externally baffled ridge vent for such conditions. At the joint of the lower roof to the upper wall siding, install Air Vent's Flash FilterVent, an externally baffled ridge vent for such conditions.

Another option is to add 1-inch-thick XPS or polyiso to the ceilings and cover the insulation with new drywall.

Q. Seven years ago, Bath Fitter redid my bathroom with an acrylic tub surround. The acrylic has Microban.

About two months ago, I noticed what I think is pink mold or mildew on the caulking, not the acrylic. When my wife or I wipe it with a cloth, it comes off, but it comes back in a few days. Last week my wife used a mixture of bleach and water. That cleaned it off, but it is coming back. The bathroom has an exhaust fan in the ceiling above the shower.

What is the pink, and how can I eliminate it permanently?

A. The pink matter is a form of mold. If it comes off easily, the mold has not penetrated the caulking itself. You are fortunate, and your best option is to dry the caulk after each shower.

If it took seven years for mold to develop, it sounds as if the caulking may have contained a mildewcide that has finally worn off. Unfortunately, I do not know of any way to restore it.

Most likely silicone was used, and it is prone to the formation of mold.

• 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.

2012, United Feature Syndicate Inc.

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