Posted by: "songbird97520" songbird97520@yahoo.com
> - I want to put a dormer in the upstairs of my 1 1/2
> story farm house. What is entailed in this project?
> I am trying to do a materials cost estimate so I can
> even decide if we can do it this year.
Hi Aliza;
You can probably have a local lumber yard put together
a materials list from a basic drawing. They usually do
that. However, without details, they will be generally
guessing, using standard materials.
> The dormer will be either one 30' dormer taking up most
> of the roof on the back of the house or 3 ~8' dormers.
You need to pay attention to the structural integrity.
Your roof, now, probably creates a triangle, with the
floor as the bottom side. That is a stable geometric
shape, even when the corners are hinged. The new vertical
wall of the dormer adds another side to it, so that the
geometry is no longer stable. Pressure (like snow or wind
loading) on the other side of the roof, will tend to push
a long dormer over. So, you need to create a new triangle,
working like only three sides again. If you will have
a flat ceiling, it can achieve that, by tying the roofs
together. You can also tie it together with collar ties,
or a couple of beams. The roof sheathing will provide
quite a bit of stiffening, but such roofs are still at
risk of a sagging ridge. You may be able to add ridge
support, down through walls, to the floor, lower level
walls, and on down to the foundation. But, you need to
know how the structure works. So, involve someone who
understands that kind of thing, and make sure that they
address these issues, under full design loading. Just
because it feels sturdy on a nice sunny day, does not
mean that after a few years of intermittent loads of
tens of thousands of pounds from wind, snow, etc, that
it will not begin to develop a sagging ridge. I know
of a few houses that have added dormers, which now
have saging ridges, and slightly out-tipped dormer
walls. So remember; if it is not a triangle (or the
sturdy, unhinged, extension of one) so that it can
bear the roof loads on the exterior walls, then it
needs to have bearing posts (or walls) under it,
to carry the load down to an interior foundation.
> Dormers will be about 6 feet deep and just simple
> shed dormer on the back of the house. House is 40'long.
The tip-up roof dormer, that was suggested, will work.
Just be mindful of structural issues.
> I am not talking about foundation support or interior
> wall issues.
Again, it may be advantageous (and even easy) to add
interior ridge support down through walls. It is likely
that there is an interior bearing wall, on the main
story, basically running down the middle, under the
ridge. If the main floor is over a basement or crawl
space, there is likely to be another beam, down the
middle of it.
You can also use this opportunity, and additional
space, to upgrade the energy performance of your
home. If you fur down the ceilings, to provide a
space for 12-16+" of insulation, you can have it
blown full of dense packed cellulose, which does
not require roof venting. Use at least 2x6s in
your new exterior walls. The walls can also be
dense packed with cellulose. Cellulose is not
expensive, and it is often cost no more to
have it installed professionally, as to
do it yourself.
Another energy area is your windows. If they
face South, they can have a positive energy
effect. If they face North, they will lose a
lot of heat during the heating season, without
gaining heat from the sun. This difference can
be around 200,000 BTU (several dollars of propane),
per year, per square foot of window. East and West
facing windows are another issue. They do get some
Winter sun, but their problem is the large amount
of Summer sun they get. So, if you have a choice,
put the dormer, and its windows facing South.
Laren Corie-
Natural Solar Building Design
and consultation, since 1975
www.ThermalAttic.com
Read my Solar house design articles in:
-Energy Self-Sufficiency Newsletter-
www.rebelwolf.com/essn.html
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http://groups.yahoo.com/group/LittleHouses/
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