Friday, April 17, 2009

Cantilevered Roof

When you know almost nothing about something, anything can seem unusual. It's why I wish I had the architect who designed the House of 42 Doors and the head carpenter who built it here, right now, so I could ask them, "Why?"

Our attic floor is framed with 2 x 6's and then covered over with tongue and groove pine boards. At some point the previous owner pulled up the majority of the floor boards and put fiberglass batts beneath them. This was no small task. The boards were nailed through the tongue at an angle and somehow he was able to take out the boards without destroying them. I'm not sure how he did it, but it's impressive. When he nailed them back down, he nailed them down through the top, rather than through the tongue.

What he didn't know was that insulating the attic in this manner was a mistake for two reasons. First he never air sealed any of the cracks in the house. This allows cold air to circulate throughout the gaps in the walls and up into the attic. Second, it's not a good idea to insulate around knob and tube wiring. It can overheat and begin a fire. It is also the only insulation in the house, a whopping R-19 in a climate that is recommended to have R-49.

We replaced the knob and tube wiring last year, so before adding any further insulation, I wanted to seal up the cracks in the attic. Several months ago, I mentioned in passing to my father that I wanted to take up the attic floor and air seal the cracks up there. He came up to help me do that, but things are never as easy as they look.

To understand why this wasn't going to work, it will take a few pictures. Roofs on most houses are built something like this.

The roof rests directly on the outside walls of the house. In this case, if there is an attic floor, the entire attic floor can be taken up without affecting the roof. It may be advisable to keep the floor in place to help tie all the joists together, but the roof can stand without an attic floor.

Our house is built like this.

This shows that when the house was built, they first put down the attic floor joists. Next was to put down the tongue and groove pine. Around the perimeter of the house they then nailed a 2x8 board, and the roof trusses are notched to rest on this. Essentially, we have a cantilevered roof, resting on the attic floor.

This makes taking up the attic floor impossible at the edges of the house where the tongue and groove flooring runs perpendicular to the 2x8. We can take up the rest of the attic floor, but if we try and take up those attic boards, the roof will fall down. Which leads me back to my original question. Why on earth was it built this way?

Besides the fact that I can't take up the attic floor (which is annoying), it has caused parts of my attic floor to bow down at the edges. The weight of the roof is really heavy over the outer eaves. This does not seem like good a good design to me.

In the end we didn't, pull up the attic boards. What we did instead I'll leave for another post.

And on the topic of straightening warped boards, I came across this suggestion. I'll let you know how it works out once I get a hot summer day.

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