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Replacing insulation on old 1.5 story house

I have a 50 year old house with pratically no insulation left. I have a question about the insulation between the side attic and the top attic.

The side attic is 40' long, with 10 inch joists, and a 4 foot knee wall. I'm going to seal off the joist space that leads under the living area, use R13 insulation on the knee walls, R30 insulation between the joists, and add a radiant barrier (perforated) along the rafters and over the knee walls [over the insulation].

The TOP attic is also 40' long, with 6 inch joists, and is 12 feet wide. I'm adding radiant barrier, and using two layers of insulation (R19+R13).

Between the SIDE attic and the TOP attic, along the rafters, there is a 5 foot slanted section of that is part of the interior room's ceiling. It looks like it has R13 (3.5") insulation with a foil backing on both sides of the baffle. It is in very poor state, including tunnels created by squirrels that lived in the attic for years (I just bought the house).There is no plastic baffle to ensure good airflow from the side attic to the top attic, although there IS some air flow.

Am I better of just leaving it as-is? Removing it and trying to re-insert something sounds like it would be a nightmare, but I'm thinking that no amount of insulation on the top and side attics will make up for the heat that will slip in through this section of the ceiling.

Any suggestions? This is Texas. We hvave 40-60 days of 100+ degree heat each summer. I include a picture of the insulation in question. I've pretty much removed all the other insulation. I've included a picture of the insulation in question.


Re: Replacing insulation on old 1.5 story house

Hi, DavidH1, my name is Doug Walden – I’m new to This Old House Discussions and just wanted to introduce myself. I’m the product manager of air sealing at Owens Corning – so happy to help you answer question about insulation.

First off – and I’m sure you have already done this – but you should locate and fix the opening where the pests were getting in. The easiest way would be to call a pro to come take a look and ensure that it’s properly addressed.

Now in terms of your insulation, it sounds like it’s definitely an issue worth fixing, but can you repost the image? It doesn’t appear to be posted on the board right now and it’d really help to see what you’re working with. You may be able to simply replace the old R-13, but I just can’t tell at this point.

Before installing any insulation though, I’d recommend air sealing leaks in attic plane. There is an air leakage path that happens between the top of a stud-wall and the drywall/plaster. Air enters a wall cavity through a light switch or electrical outlet, travels up the wall cavity and escapes into the attic between the stud and drywall/plaster. Sealing this can reduce drafts in your house, save energy (savings vary) and make the insulation more effective. Not to sound too commercial, but Owens Corning has a product called EnergyComplete Sealant that is made for this exact purpose. Not sure of your level of expertise, but unless you’re a professional, I recommend finding an experienced contractor in your area to install the sealant – I know we have many in Texas who can help.

Hope this helps for now. I’ll be able to provide more info with a picture and will look for your response.

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