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Ask the Remodeler: A home with a mansard roof needs insulation. But what kind?

Ask the Expert Spring House Hunt
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Q. We are the new owners of an 1870s Second Empire Victorian. Our attic is well insulated, but the second-floor walls — behind the mansard roof — are uninsulated. A Mass Save energy auditor suggests blowing in cellulose insulation. Since the exterior “walls’’ are actually roof, what is the best practice for insulating this space — both in material and process? We want to ensure we don’t create problems with moisture-retaining materials that can lead to rot or mold growth. Also, most of our siding is the original clapboard, with a few pieces of newer clapboard mixed in. The original siding seems at the end of its life, with lots of split boards, etc. Instead of continuing to paint and patch (at moderate expense), at what point does a full siding replacement make sense? If we replaced the siding, would cementitious siding perform well on a building like this, or would new wood clapboards be better?

J.B., Newton

A. Assuming the mansard roof is tight, blown-in insulation is a good, cost-effective way to get some insulation in there. Mansards are so steep, they are more wall than roof, and we have been using blown-in for years without any problems.

A more effective insulation, however, is Icynene, or foam insulation. Closed-cell is the best. It has a higher R-value (the scale by which insulation effectiveness is measured) and acts as a vapor barrier; moisture does not travel through it. Be aware that you will have to open up the walls from the inside entirely to use closed-cell.

A less invasive option is open-cell foam. Its R-value is not as high, and it does allow some moisture to pass through it. But if you use open-cell, you can open up just the middle portion of the wall, spray the foam into the cavities above and below the opening, and then fill the opening. The reasoning here is that closed-cell gives off too much heat to spray behind the wallboard, but open-cell does not.

Determining when to replace siding typically is subjective. If you don’t mind having it touched up every three years or so, then keep the old siding. Properly maintained, it will outlive all of us. Some people do not want the bother and want all new and to paint the house every seven to 10 years (depending on the climate). Cement or composite siding materials are fine for either an older or newer house. There are a lot of good, green products coming on the market that are more stable than wood and will hold paint longer.

 

Q. We have two Casablanca ceiling fans that were put in as part of an addition to our home about 30 years ago, and they still work fine except that I worry about them wobbling now on higher speeds. One of them is over our bed. Could it fall? Whom should I call to inspect them? Thank you.

PEG, Whitman

A. I would call an electrician to look at the fans. They are old and may need to be replaced. Sometimes they just need to have the blades adjusted with little stick-on weights that help balance the fan blades. A qualified electrician could also check to see whether the fan motor itself is anchored properly and whether there is proper blocking or framing in the ceiling.

Mark Philben is the project development manager at Charlie Allen Renovations in Cambridge. Send your questions to [email protected]. Questions are subject to editing. Subscribe to the Globe’s free real estate newsletter — our weekly digest on buying, selling, and design — at pages.email.bostonglobe.com/AddressSignUp. Follow us on Facebook, Instagram, and Twitter @globehomes.