This space is tall enough to walk in and I wanted to keep it a warm space for storage so I chose to insulate under the roof as opposed to insulating the floor and knee walls. I explained how I came to that decision in an earlier post.
I started off with 4x8 sheets of foiled backed polyisocyanurate- or Thermax or Tuff-R.
I hauled them home on the roof of the Passat.
I pulled them upstairs and got to work.
As I explained in an earlier post, I wanted a 1 inch air space between the roof and the insulation. There has been some debate as to whether or not that is needed but I decided to go with it. To create the airspace, I first used some 1/2 inch x 1 inch long boards nailed the full length of the rafters but that involved using a lot of wood and was going to add a lot to the cost. I decided I could use pieces of the insulation. So I cut that into lengths about an inch wide and used them to provide the spacing for the air gap.
I used adhesive to secure it to the rafters. This would prevent the insulation panels from making contact with the roof boards.
I pulled them upstairs and got to work.
As I explained in an earlier post, I wanted a 1 inch air space between the roof and the insulation. There has been some debate as to whether or not that is needed but I decided to go with it. To create the airspace, I first used some 1/2 inch x 1 inch long boards nailed the full length of the rafters but that involved using a lot of wood and was going to add a lot to the cost. I decided I could use pieces of the insulation. So I cut that into lengths about an inch wide and used them to provide the spacing for the air gap.
I used adhesive to secure it to the rafters. This would prevent the insulation panels from making contact with the roof boards.
In retrospect, I should have applied the pieces to the whole length of the rafter. This would have sealed the area better. I had plenty of scraps of this stuff so there was no need to break it apart and space it like I did. My goal was to have no air infiltration from the ridge and soffit vents in to the attic space and using one long strip would have helped.
I measured between the rafters and cut each piece of polyisocyanate to fit. The rafters are approximately 3 1/2" wide. So there was one inch of air space and 2 pieces of polyisocyanate between the rafters.
It was very easy to cut and work with, lightweight but it was time consuming measuring and cutting each individual piece. I put the shiny aluminum side facing the roof rafters on the first layer but I was unsure about the second layer.
I decided to face the second layer out. I fitted each layer between the rafters. I filled any gaps with expanding foam insulation and then taped all the seams with foil tape.
It certainly made the space much brighter. I then used full sheets to add another layer of insulation on top of the rafters. I used screws and 1.5" plastic washers to hold the third layer up on to the slanted surface.
It was very easy to cut and work with, lightweight but it was time consuming measuring and cutting each individual piece. I put the shiny aluminum side facing the roof rafters on the first layer but I was unsure about the second layer.
I decided to face the second layer out. I fitted each layer between the rafters. I filled any gaps with expanding foam insulation and then taped all the seams with foil tape.
It certainly made the space much brighter. I then used full sheets to add another layer of insulation on top of the rafters. I used screws and 1.5" plastic washers to hold the third layer up on to the slanted surface.
East side of the attic:
West side of the attic:
All the furniture and stuff from the sewing studio is packed in here as I work on painting and replacing the carpeting.
Lots of cutting and fitting was needed to work around the studs in the knee wall. Well, it is a lot taller than a knee wall.
Lots of cutting and fitting was needed to work around the studs in the knee wall. Well, it is a lot taller than a knee wall.
And that is how I insulated my attic!
2 comments:
Boy, that attic space looks familiar!
How has this installation worked out? Warm enough? No condensation? I was trained as an architect, but somehow even for me all the theories about heatflow and moisture infiltration come off like so much conflicting mumbo-jumbo. Which one makes the most sense to me seems to vary with the time of day and the phase of the moon!
So, they say that one should have only one vapor barrier (your shiny foil) in any one build-up of insulation, and the VB should go towards the warm side. Otherwise, they say, moisture can build up between the layers and degenerate the insulation. Have you noticed anything like that?
I won't be putting any insulation in the knee wall, since I want to maintain a more or less equal temperature between the storage space and my study. The important thing, I've definitely learned, is that the conditioned spaces, including the attic storage, must be kept within the building envelope. The roof insulation achieves that.
Since you already had ridge and soffit vents, keeping the airspace was probably a good idea. I doubt my house has ever had either, so the foam will go smack against the sheathing for an airtight installation, per current Code.
Great how-to post!
Kate H.
www.sowsearhouse.blogspot.com
Wait a minute. The later pictures make it look like there's shiny insulation on the knee wall. But you weren't going to put it there. Is that just a trick of the light?
Kate H.
www.sowsearhouse.blogspot.com
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