I'm in the process of getting estimates to have vinyl siding installed on a 1950's house. Under the wood siding is that black Homasote type fiber sheeting. One of the contractors pointed out that this type of siding isn't structural and once the wood clapboards are removed it should be over-sheeted with plywood or OSB. Is he correct or just trying to sell me something else?
Homasote Fiberboard under siding
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James Henry
In the Trades
Homasote is worthless for strength. if you have plywood on all the corners and maybe every other sheet of the house that's good enough.
Look for cut-in braces on the corners also. consider some kind of wrap for the house. Go online and do some research. Call around and get some opinions.
Look for cut-in braces on the corners also. consider some kind of wrap for the house. Go online and do some research. Call around and get some opinions.
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If the fastener spacing and type meets spec 1/2" & 3/4" asphalted fiberboard meets a structural standard (see Figure 1) , even though it's not as robust as plywood/OSB or plywood/OSB shear panels spanning the last two stud bays on the exterior corners. It probably won't meet Florida's current hurricane resistance standards without further reinforcement, but your studwall and roof anchoring probably doesn't meet it either. Now would be a good time to assess that.
Asphalted fiberboard is highly water tolerant, and does not need a housewrap, but it takes a roof-repair type caulk to adequately air seal it. Fiberboard sheathing also adds about R1 "whole wall" to the thermal performance of the assembly compared to a plywood or OSB sheathed building. R1 may not sound like much, but it's a 10% improvement over an 2x4/R11 type wall.
Now would be a good time to assess the wall insulation and air tightness too- it's pretty easy to blow fiberglass insulation in over R7-ish "econobatts", or even low density R11s to improve both air tightness & R-value. Blown fiberglass follows the air leakage paths, clogging them up considerably. Even at 1.3lbs density it makes a real difference. Going more than 1.3lbs density risks bowing out the fiberboard, but if re-sheathing with OSB or plywood dense packing to 1.8lbs would bring it up to R15 in the cavity, with measurably better air-retardency.
Asphalted fiberboard is highly water tolerant, and does not need a housewrap, but it takes a roof-repair type caulk to adequately air seal it. Fiberboard sheathing also adds about R1 "whole wall" to the thermal performance of the assembly compared to a plywood or OSB sheathed building. R1 may not sound like much, but it's a 10% improvement over an 2x4/R11 type wall.
Now would be a good time to assess the wall insulation and air tightness too- it's pretty easy to blow fiberglass insulation in over R7-ish "econobatts", or even low density R11s to improve both air tightness & R-value. Blown fiberglass follows the air leakage paths, clogging them up considerably. Even at 1.3lbs density it makes a real difference. Going more than 1.3lbs density risks bowing out the fiberboard, but if re-sheathing with OSB or plywood dense packing to 1.8lbs would bring it up to R15 in the cavity, with measurably better air-retardency.
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