Another Overhang Insulation question


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Old 09-17-18, 08:40 AM
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Another Overhang Insulation question

Last year we had a very cold week in Northern NJ with many days below zero. Well I had a frozen pipe and I was able to eventually find it in the overhang. No idea why this builder put the pipe in the overhang but he did and since I was running two fireplaces I guess the water in the radiators didn't cycle enough and it froze solid. Anyway, when I opened up the overhang I noticed two things, one was the stupid pipe location and another was how the overhang was only insulated with very little fiberglass insulation and that was only being held up by a soffit material so all sorts of air was flowing into my first floor.

Anyway, I have been looking online on how to insulate it correctly so I am going to get 2 inch foam board and block the opening into the floor joist and also place it directly onto the subfloor and box the whole area in then fill the rest of the void with fiberglass insulation before then using the foam board on the bottom of the joists to reduce the thermal bridging.

I have two questions though, will I have any issues with condensation issues if I make a airtight box with the foam board?

Also, what is the best way to insulate around the pipe to lesson the chance of a freeze up again in the future? Right now it just has the black pipe foam over it.

I attached the picture of what i saw when I first open up the cavity and pulled down the fiberglass batt.

Thanks a lot!
 
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Old 09-17-18, 09:33 AM
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The airtight box is not the way to go. Basic guideline is to insulate between the pipes and the cold but leave the pipes open to their heat source, in this case I'm assuming those joist cavities.

Where the air sealing becomes important is preventing outside air from leaking in anywhere. Adding more rigid below the joist is good, but one inch might be sufficient. Remember it only failed under extreme conditions and the basic improvements I suggested are a major upgrade.

I'm not fond of fiberglass just don't add it where it might limit the heat reaching the pipe.

I'm assuming a warm basement, if cold crawlspace I would change my suggestion.

Bud
 
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Old 09-17-18, 09:54 AM
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Thanks for the reply Bud. Only two bays have the heat pipe within them, so you are saying i should only have the rigid foamboard on the bottom of the joists in that area? Should I box in the rest of the joists like I explained or just put in the 1 inch foam board down the bottom of all joists and call it quits?
 
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Old 09-17-18, 10:23 AM
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You want to insulate below the pipe including the outermost area but the pipe itself will be exposed to the interior warmth so it wont freeze!

Actually this is a very common situation !
 
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Old 09-17-18, 10:46 AM
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Heating with wood can be a disaster for baseboard hot water. A friend here in Maine had his pipes freeze and then unfortunately thaw when the family was away. Boiler kicked on to replenish the escaping hot water and destroyed his house with steam. Hardwood floors looked like a roller coaster an all drywall was down or sagging. Point being, cycle the water through the system under some planned intervals.

For the full length of the overhang insulate the outer band (and two ends) with either rigid foam or where the pipes are with Roxul, very dense and tight when fitted into place. Add rigid between the joists at the bottom and then cover the entire bottom with another layer. Basically you want at least one layer of rigid insulation against all exterior cold surfaces.

Note, the pipe insulation is there to reduce heat loss from the heating pipes not intended to eliminate freezing, but may help, it it doesn't hurt by isolating the pipe from the heat in the basement.

If my description is lacking don't hesitate to ask. Many here are pros on this issue and will add more info.

Bud
 
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Old 09-25-18, 03:53 AM
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This weekend I plan on doing this project and want to make sure I am doing this correctly. I have been looking on the internet and see people doing this multiple ways. I am going to totally eliminate that one heat pipe from the cavity so I won't have to worry about plumbing issues anymore. I have seen people take the foam board and close up the cavity that runs through the house. Should I be doing that as well? The cavities run through my unheated garage so I am not sure if leaving them open or closing them up would be beneficial to keep it warmer in my bedroom above.

Also, I have seen other people put the foam board directly under the subfloor rather than at the bottom of the joist. Why is there so many ways of doing this? You would think there would be one best way of going about this project.

Anyway, thanks for the help!
 
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Old 09-25-18, 08:47 AM
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You would think there would be one best way of going about this project.
There is, seal and insulate against the cold surfaces up to the pipe.

That will eliminate/minimize cold intrusion into the house/joist area/overhang but then leave the pipe exposed to the warm air so it will not freeze.

Again, a very common construction/plumbing situation but easy to solve!
 
 

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