Working towards a future of almost non-existant heating and cooling bills!
In my house the pitch of the roof is 17 degrees.
That is very shallow. When I got the soffit open
I got a good look at how the roof was put
Copyright 2013 Eco Houses of Vermont, LLC
The people who built my house made a roof truss on site. This screen shot of a sketch up drawing I made shows how they
did this. The ceiling joist juts out to the end of the eaves. The roof rafter is cut at an angle and sits on top of the ceiling joist.
There is a small wedge shaped piece of 2x4 which fits in between the joist and rafter.
Chris West is a Certified Passive House Consultant
Affiliated with the PHIUS and PHI 2013
Scaffolding rented from local equipment rental
place. Two seven foot sections, two high. Gives me
the ability to leap-frog them.
What is a soffit? It is the underside of the eaves. When you look up at
the eaves from the ground it is the part you see. In my case the soffit is
horizontal to the ground and painted white with a vent for the vented
The soffit is usually created by adding a piece of thin plywood to the
underside of the ceiling joists that stick out above the wall.
November 9, 2012
Deep Energy Retrofit in Jericho, Vt!
Part 2 - The soffit work begins
The point of the Chainsaw Retrofit is to cut the
ceiling joist so that it doesn't act as a thermal bridge.
In this instance the 2x4 of the ceiling joist can act as
a heat sink fin, similar to the fins you see on a lawn
mower. The difference is the ones on the lawn
mower are there on purpose to help the motor
release excess heat created during internal
combustion. In a house it is an unintentional loss.
People just didn't think of the ceiling joist as a way
through which the house could loose heat. But it is.
So this is what we want the ceiling joist/roof rafter assembly to look like. The yellow block is six inches of Poly Isocyanic
insulation. This material has an R-value of 6.2/inch. With six inches that board has an R-value of 37.2. The reason we want
the insulation board to go up into the ceiling joist is to create a continuous layer of insulation.
The attic is full of blown cellulose. The contractor is going to fill the
area between the poly iso board and the cellulose with a layer of
spray foam. This will act as an air sealing as well as connect the poly
iso and the cellulose layers. More on that later.
First pics of the real work.
This is what I saw once I had the soffit opened.
What we see here is the ceiling joist and the roof
rafter coming together. The piece of plywood that is
naied to the two of them is a gusset - a piece of
wood (plywood, osb, etc) which is used to tie two
structural members to one another.
This gusset is made of 3/8" plywood. There is one
on either side of each ceiling joist/rafter connection.
The gusset is held in place using 1" long staples.
you can see there are quite a few of them.
The next few pictures show the sequence of making
the cutout in the ceiling joist.
Cut the back of the gusset flush to top plate.
Here is the cut the multi tool made.
Marking the outline of the rest of the cutout.
The pencil outline of the cutout we want.
Saws-all the first bit out.
Doing it in bits.
First bit out.
Finished cut out.
Now just repeat that forty times or so.
The last step is to put a layer of OSB or plywood between the joists to do the job that the fiberglass insulation
was doing - namely keep the loose fill cellulose in place.
I am working on some Therm models to show the psi value of the different constructions:
- Wall to Roof detail as it was in the house before the chainshaw retrofit.
- Wall to Roof detail after the retrofit and the addition of the poly iso insulation.
Next step: Moving the front stairs and deck away from the house to have clearance for the 6" of insulation.
Eco Houses of Vermont, LLC