GUEST, in Hotton’s chat room

A. . . . And disintegrates, and any rodent can tear it apart. For one thing, copper or stainless steel “wool” will work, but it has to be very tight lest the critter pulls it right out. Sometimes the space between wall and wood sill, or between sill and foundation can be quite large; besides, a rodent can get through a very small space. I think working from inside will be easier. You can fill voids with mortar, or tightly with a rope caulk, or rolled up aluminum screening, again, very tightly inserted. If you try caulking, most compounds will not stay in place, but an adhesive caulk will. Phenoseal and Polyseamseal are two good ones, and will really seal the joint.

Q. I need to pour a small concrete pad (16-by-31 inches) for a ductless AC compressor. I was told to put crushed rock down first. Do I pour the slab on top of the rock or onto the bare soil that is underneath, then fill around the crushed rock? NICK, in Hotton’s chat room

A. The slab goes on top of the crushed rock. Dig a hole at least 12 inches deep and fill it with 6 inches of crushed stone. This will allow drainage. Then set your frames and pour the slab 12 inches thick. This will allow the slab to be fairly stable in winter, able to resist the pressure of frozen earth, and incidentally allow the slab to stick 6 inches above the ground. Twelve inches may be a little extreme, but it won’t hurt to do.

Q. I had a new gas boiler installed in my 39-year-old house. I have always had gas as a fuel, so this is not a change, only a new unit. The installer did not put a stainless steel liner in my chimney. Why not? You often mention when a gas burner is installed in a house, a stainless steel liner is required. CURIOUS

A. At first I thought this was strange, but then I realized your new unit was the same gas burner as the old, and that you did not change the fuel. Therefore it might be grandfathered, and not subject to rules requiring a new liner. Check with your local building inspector.

Q. My dad and I own a rather large old building with offices and other companies, and in summer the heat is horrible. What are inexpensive ways to keep the building cool? The building has a lot of windows. When we wash them, how can we reach high ones? J.G., Framingham

A. The only inexpensive cooling system is moving air with fans, which doesn’t work well when the heat persists through the night and all day. Air conditioning is expensive, and I don’t think you should attempt that until you have a plan for insulating the building: walls, attic floor, basement ceiling, and sometimes the interior walls as well, which will allow better distribution of cool air and promote sound control as well. So, consult an insulation company, who will analyze your needs and make a proposal on what the company will do. Also, consider storms on all those single-glazed windows. Or consult a window specialist.

If the windows are not above the second floor, an extension on the brush will work. It might also work if you hire a window-washing company.

Q. I want to pull up old carpet on wood stairs and I have no idea what’s underneath. How should I prepare other than a power sander and some stain? JEFF, in Hotton’s chat room