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Roof Above a Roof? Mac the Nice 07-17-2007
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Posted by Mac the Nice on July 17, 2007, 1:37 pm
We are presently restoring a 1,250 sq. ft. log home built in the early '70s,
sited on a spot without a leaf of shade over the roof. The pitch of the
original roof (built of trusses) is approximately 1:4 which strikes us as
being pretty low even for the southern Missouri Ozarks where there is now
and again a fair amount of snow come winter, and the avg. yearly precip. is
43.6 inches.

The structure was built of oak logs from 6 to 10 inches in diameter and
raised in three stages--leaving a central, original structure of 28 x 22
with later log additions either side 25 x 14. Standing in front of the
place you're looking at an overall log-built broadside of 50 feet with north
& south additions indented by three feet at the front, but forming an even
exterior at the back. The roofs over the north and south additions are
approx. one foot lower than that of the original central building.

We want to frame one roof (at an increased pitch) over the entire building,
leaving the original roofing in place. We would superimpose new ridge beams
and rafters from either side of the stone masonry chimney to both gable ends
about two feet higher than what's there now, to leave at the peak that much
ventilated air-space covered by Ondura corrugated asphalt impregnated
fiberglass--with no plywood sheathing, but a framework of planks over
rafters (16" on center) spaced about 8 inches--wider if feasible.

This would be ventilated from both gable ends and at the soffits, and
further so by fans installed at gable vents.

In short, we want to build a condition of shade over the original roof. Can
this be done, or are we just dreaming like the pair of amateurs we are? If
otherwise it seems a sensible plan, we'd want to remove those three layers
of baked, crumbling shingles from the original roof surface and put down
some form of rigid insulating material, such as the commonly available
foil-faced sheathing or whatever would stand up to the heat--there would be
at least 6 inches of ventilated air space at the new soffits between the
corrugated roofing and the insulation sheathed original roof.

Can this work?
--
Mackie



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Posted by marson on July 18, 2007, 10:33 pm
wrote:
> We are presently restoring a 1,250 sq. ft. log home built in the early '70s,
> sited on a spot without a leaf of shade over the roof. The pitch of the
> original roof (built of trusses) is approximately 1:4 which strikes us as
> being pretty low even for the southern Missouri Ozarks where there is now
> and again a fair amount of snow come winter, and the avg. yearly precip. is
> 43.6 inches.
>
> The structure was built of oak logs from 6 to 10 inches in diameter and
> raised in three stages--leaving a central, original structure of 28 x 22
> with later log additions either side 25 x 14. Standing in front of the
> place you're looking at an overall log-built broadside of 50 feet with north
> & south additions indented by three feet at the front, but forming an even
> exterior at the back. The roofs over the north and south additions are
> approx. one foot lower than that of the original central building.
>
> We want to frame one roof (at an increased pitch) over the entire building,
> leaving the original roofing in place. We would superimpose new ridge beams
> and rafters from either side of the stone masonry chimney to both gable ends
> about two feet higher than what's there now, to leave at the peak that much
> ventilated air-space covered by Ondura corrugated asphalt impregnated
> fiberglass--with no plywood sheathing, but a framework of planks over
> rafters (16" on center) spaced about 8 inches--wider if feasible.
>
> This would be ventilated from both gable ends and at the soffits, and
> further so by fans installed at gable vents.
>
> In short, we want to build a condition of shade over the original roof. Can
> this be done, or are we just dreaming like the pair of amateurs we are? If
> otherwise it seems a sensible plan, we'd want to remove those three layers
> of baked, crumbling shingles from the original roof surface and put down
> some form of rigid insulating material, such as the commonly available
> foil-faced sheathing or whatever would stand up to the heat--there would be
> at least 6 inches of ventilated air space at the new soffits between the
> corrugated roofing and the insulation sheathed original roof.
>
> Can this work?
> --
> Mackie
>
> --
>
> .............................................................
> > Posted thru AtlantisNews - Explore EVERY Newsgroup <
> > http://www.AtlantisNews.com -- Lightning Fast!!! <
> > Access the Most Content * No Limits * Best Service <

Yes it can be done. All it takes is money. Probably quite a bit.
Without seeing it, I'm just guessing, but you would probably need to
add new intermediate posts with associated footings to hold up the new
ridge beam. Also would need to set the rafters on something. Doesn't
really seem practical. Scissor trusses might be an option, but even
there, framing a new roof on top of an old roof is bound to be
expensive--Not a great payback IMO.


Posted by Mac the Nice on July 19, 2007, 11:25 am


> Yes it can be done. All it takes is money. Probably quite a bit.
> Without seeing it, I'm just guessing, but you would probably need to
> add new intermediate posts with associated footings to hold up the new
> ridge beam.

Makes sense. Whereas merely trying to tye in to the old end trusses is not
such a solid idea. I can see what you mean. But as to those intermediate
posts, as it happens we've got four of those already worked into the design,
as I was running it down in another post . . .

Subject: Re: Shading a Roof--with a roof?
Date: Wednesday, July 18, 2007 11:43 AM


> Sounds like a good plan.

Glad to hear it.

> It would keep the original attic cooler in the
> summer and provide a cold roof for the winter - no ice dams, if they were
> a
> problem in the past.

Maybe you heard about that ice storm of last winter--worst in anyone's
memory for the area? All the firewood needed for years to come is now at
everybody's doorstep. Driving through it this spring while the trees were
yet bare, one word kept coming to mind: Tunguska!

As to the attic, yes, that's the main idea--but you should see it as it is
now, all crowded up with those 24 foot trusses spaced at 16" on center,
about which I neglected to mention the really hairy part and the reason we
got the place so cheap, why *zero value* was being assessed to the house,
which according to the realtor was "built too low"--with that drywall
ceiling only 6' 6" above the floor?

Lordy! Little wonder the bank that repossessed the place saw land value
alone at their price of $39,000. So, when they finally caved to our bid of
$31k, not only did we get a free log home (worthy of Snow White and the
Seven Dwarfs) with that 20 wooded acres, but the electric installation, the
well and working submersible pump, even the septic system to boot.

Obviously, except some caterpillar from Alice in Wonderland should happen
along to offer us a bite of something magic to raise that ceiling over our
heads, something else has to be done about those trusses, especially as it
comes to the project of providing the semi-cathedral style ceiling we want
for the place. The rafter (top chord) span is 16 feet from plate-log to
peak. They are 2x4's. Our plan (or should I say "our hope") is that we can
raise the horizontal bottom chord with its triangular webbing up to the 9'
level, three feet below the peak--without having to break up the living
space with unwanted bearing walls to keep those trusses firmly in place.

Obviously, some form of support must be had to stop those unsupported rafter
legs of the trusses from sagging, so I figure to raise two stout purlins
(paired or trebled 2x8's) to run parallel with the plates that formerly bore
support for the trusses, these would now bear that load, as bolted to 6x6
upright beams--just two per purlin, equally spaced as raised from piers
under the house up to that nine foot level.

I did this once upon a time back in the 60's for a house full of mushroom
munching dwarfs (aka "hippies") along the Avenue of Giants in the Northern
California redwood country, north of Mendocino and it seemed to work pretty
good. It was my proudest achievement of those years, as a 'hippie', that one
8 by 8 beam I installed in that house, from a hole in the ground beneath the
floor and up to the sky, to the second story they wanted to add. Initially,
I'd wanted nothing to do with the project, till I was out-voted and the
State of California came by to say there'd be no permit without that beam
should go into the ground right beside my bed.

Beside *my* bed? Yup. So said the Law. Well, all right then. Since it was
beside my bed that the law said a log had to go, I made it my project to see
to it that it should go up straight and true, so the roof should not come
down over me and my old lady's head--and I did it right, smoking nothing
more aromatic than tobacco while I was at it, mixing the cement and framing
the braces. I believe that beam still stands in the middle of the redwood
forest there in the middle of that hacienda as a monument to a moment of
sobriety in the midst of a year long orgy of nothing of the sort.
--
Mackie http://members.virtualtourist.com/m/520b8/

> Also would need to set the rafters on something. Doesn't
> really seem practical. Scissor trusses might be an option, but even
> there, framing a new roof on top of an old roof is bound to be
> expensive--Not a great payback IMO.

No time now, but I'll get back with this tonight.
--
Mackie



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