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Remove compressed insulation or leave it there?

I just bought a house in New Hampshire where the previous owner had started finishing the garage built with 2x4 walls using R-19 insulation. He stuffed it in there pretty well and stapled it down, but it bulges like crazy and is ripping free in spots. He did not add the vapor barrier or drywall/plywood over it. I know he should have used R-13 insulation for the correct fit.

My question is, which is better R-13 insulation or R-19 insulation that has been compressed 2" further than it should have been? I'm trying to decide if I should remove all the R-19 and replace with R-13 or just finish the wall leaving the compressed R-19 in place and save the money. I know I'm not getting R-19, but is the compressed R-19 just as good or slightly better than regular R-13? It's a two car garage and would save me probably a few hundred dollars if I can leave the R-19 in place.

Re: Remove compressed insulation or leave it there?

Insulation is not supposed to be compressed or bulging. You can save money by removing the existing insulation (be gentle with the staples) and re-installing it correctly, adding a vapor barrier, with new staples. R-19 is acceptable for 2x4 walls and you don't need to replac it with R-13.
Which one is better for your area? probably correctly installed R-19.

Re: Remove compressed insulation or leave it there?

Fiberglass insulation is a balance between conduction and convection. The fiberglass strands themselves will conduct heat with little resistance, it is the length of the strands that retards the flow of heat. The strands also slow down the convection of air within the cavity in order to retard heat flow.

Increasing the density of the fiberglass further reduces the convection, but at some point, the increased surface area contact of the individual strands increases conduction. I have seen some pretty high density fiberglass installations that are quite energy efficient, but I don't know the point where adding more fiberglass to a fixed area becomes counter productive.

Off hand, I'd say that you are getting maybe slightly better R value, but no where near the R-19 that you would get if the walls were at least 7.25" thick. The installation of the vapor barrier is the key issue here. For this application, the flanges of the facing should be stapled over the ends of the studs, not against the inside face as typically done. If the facing is ripped or torn, it should come out.

If the facing is mostly good and the flanges are stapled to the ends of the studs, just tape up any tears and install the drywall. If the facing is stapled to the inside faces, remove the staples and re staple the flanges to the ends or remove the facing all together and install a plastic barrier.

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