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I have a two story 1970s home that has basically storage rooms upstairs off the bedrooms where the roof angles down. Inside these rooms is the studs and insulation facing the exterior roof. Since they are angled the bat insulation keeps falling out. It was originally stapled, but has not held up. These rooms are pretty large and we use them for storage. There is an additional attic above the bedrooms.

What is the best way to fix this sagging without completely re-doing the insulation?

It can't be stapled as that has failed and the paper is in bad shape. Could I put foam board over the top and nail it to the studs holding it in place? This would probably leave gaps at the bottom and top due to the angle.

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You have several issues: 1) hold the insulation in place, 2) vapor barrier, 3) vent space above the insulation

1) I’ve seen string installed across the joists to keep the insulation from falling down. They usually install it about 6” apart at the ends of the batts and about 12” - 16” apart elsewhere. You can staple the string to the bottom of the joists.

2) Using string will not provide a vapor barrier. If you use poly sheeting stapled on the bottom of the joists, it will provide a vapor barrier. Depending on where you live, you may not want a vapor barrier.

3) The Code requires a 1” air space above the insulation. That is to say, you must maintain a 1” air space between the bottom of the roof sheathing and the top of the insulation so air can circulate. (You’ll need to verify that attic vents are installed so you don’t get condensation in the attic.)

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  • Depending on your climate the vent space between the insulation and the sheathing may or may not be necessary. If you are in a climate where the vapour barrier isn't necessary, the air space is probably also unnecessary. It may be required by code even if unnecessary. – Sherwood Botsford Sep 21 '19 at 20:03
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    Cheapest source of string for this is baling twine. The skinny 110lb test line runs 18,000 feet per double spool, and costs 20-30 bucks. – Sherwood Botsford Sep 21 '19 at 20:04
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    Simpson makes "insulation support wire" that's basically thin springy steel rods. It might be a quicker install than string. Possible tip: home derpos near me don't stock it with insulation (where it would make sense), but rather with the rest of the Simpson hardware. – Aloysius Defenestrate Sep 21 '19 at 22:57

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