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Insulating an attic space - got a couple of questions...

Insulating an attic space - got a couple of questions...

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  #1  
Old 08-28-18, 12:03 PM
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Insulating an attic space - got a couple of questions...

I want to insulate an attic space to make it into a heated/cooled clean storage area. The house was built in 1890 and this is what I'm working with...



My thought is to place insulation between the roof rafters and then sheet rock over so the area stays clean.

My question has to do with ventilation baffles. It looks to me the insulation that is stuffed into the area above the wall is too tight and there should be a baffle in there...right? Would I need to install baffles behind the insulation all the way from the eave/soffit to the ridge? Or can I install insulation that allows air to flow between it and the roof?

Thanks for any advice!
 
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  #2  
Old 08-28-18, 01:15 PM
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Michigan has 3 different climate regions so you are looking at a minimum of r-38 or r-49 depending upon where you are. In addition, that convenient graphic is form 2009 and the codes have been upgraded in 2012, 2015, and 2018 and only your local authority knows which one they are currently following. Use the 09 as a minimum but check to see if more is required.

But the 09 is saying you will need about a foot of depth to accommodate the insulation and a gap for ventilation. Now, there are combinations of rigid foam and batt insulation that can act as your vent channel as well as reducing the total depth an inch or so.

Note, it is a code violation to install fiber insulation against the roof deck.

And yes that insulation that is stuffed in there would come out and be replaced by baffles in every rafter bay.

Bud
 
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Old 08-28-18, 05:51 PM
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Thanks Bud, I appreciate your response. The roof rafters are 2x6 so they won't allow me enough depth to get the roughly 1' depth of insulation. Is this an option... fir out the rafters with 2x2's, install batt insulation about 6" - 7" thick and then cover it all with rigid foam. I haven't done the "R" calculation to see if this will hit my requirement, but in theory, would this work?

The foam would seal the room making it clean and I would not sheet rock, saving me a step.
 
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Old 08-28-18, 06:30 PM
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Avoiding the drywall would be a local code decision. As I said, Dow Thermax is the only one I'm aware of that has gone through the testing and approval process. But I don't see everything by a long shot.

Typically the build up to reach your r-value starts by creating your air channel, 2" of rigid on edge blocks to create the air gap and then batt insulation of your choice. I like Roxul, good r-value and very dense, stays in place nicely.

In your description I don't see a specific air channel. I prefer a rigid layer between the air channel and the fiber insulation.

Bud
 
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Old 08-29-18, 04:26 AM
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Thanks again, Bud. I appreciate your expertise. It appears this house is woefully under insulated (we just bought the house a year or so ago...). It looks like I have a larger project ahead of me than just cleaning up some storage space. All good- needs to be done!
 
  #6  
Old 08-29-18, 04:52 AM
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I've been taking my 1979 cape from its 1979 construction methods up to what we call a deep energy retrofit (still more to do) but the results have been amazing. DIYing it can be cost effective, but bringing in contractors to do everything would never be justified by the savings. With DIY I get to enjoy the improvements and the savings.

As you tackle each project do your reading so every step becomes progress towards a very well insulated and air sealed home. I always hate to hear when someone dumped 2' of new insulation into their attic but didn't attend to any air sealing.

Bud
 
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Old 09-03-18, 12:40 PM
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Bud... or anyone else that wants to opine... a couple more questions...

I'm thinking the best approach to insulating the attic/ roof is to insulate the entire roof system. The house is a two story with a hipped roof. Obviously, the rafter bays in the corners of the roof do not go all the way to the roof ridge. Do i need to provide an air channel in those bays?

When you say to install edge blocks and then 2" rigid, would you use 2" for the blocks or would a smaller block be adequate? How do you install the blocks and rigid? Screws or glue?

Thanks a bunch!
 
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Old 09-03-18, 12:56 PM
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I'm painting now so will be short. I don't recall this thread discussing a hip roof but I will review later. Bump if I forget.
Search "insulating a hip roof GBA" adding GBA will pick up Green Building Advisers a class group of pros. Building science corporation is another source.

I'll be back.
Bud
 
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Old 09-06-18, 06:53 AM
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Thanks Bud, as always. It looks like from the GBA article the best solution for me is to spray foam insulation, at least in the hips. Could spray be done over the entire roof system? Probably pretty expensive...

My conclusion is to spray the hips and then do the channel system you described in the rafter bays that go to the ridge. Do I have that right?
 
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Old 09-06-18, 07:02 AM
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Not being living space I think eliminates the need to cover the spray foam with drywall or other thermal barrier, but that is a local authority decision.

A hybrid approach doesn't have a history to help identify any potential problems but from here I don't see any. The channels will provide the necessary air path for ventilation as long as you have upper and lower vents.

Bud
 
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Old 09-06-18, 07:26 AM
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Got it, thanks. I need to get a spray contractor in here and get an estimate and go from there. You've really helped me figure out the best way to insulate this old house.
 
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Old 09-06-18, 07:30 AM
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Actually another question... When building the vent with rigid foam, what size material should I use for the blocks? Is 1" enough? How to install - glue...screws?

Thanks
 
  #13  
Old 09-06-18, 08:13 AM
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One inch is minimum. I usually use construction adhesive but it needs a nail to tack the foam in place until it cures. There are many adhesives suited for foam and if you find and use a fast drying it could eliminate the nail. Roofing nails have a wide head, just select a length that doesn't go all the way through .

Bud
 
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