Home Page link

Re: Roofing Question

Home| Search | About
Login Password
Register Now! Lost Password?

Home Repair - - If it ain't broken, don't fix it. Otherwise look here. 

Page 1 of 2       1 2 > last >> Bookmark this page:  YahooMyWeb Yahoo!  Google Google  Windows Live Favorites Windows Live  del.icio.us del.icio.us  digg digg  Add to Netscape Netscape
Subject Author Date
Re: Roofing Question Wayne Whitney 04-06-2008
If you were  Registered and logged in, you could reply and use other advanced thread options
Posted by Wayne Whitney on April 6, 2008, 5:35 pm
>
>> If you are in a high wind or seismic area, you may wish to consider
>> going over all the T&G 1x with 1/2" plywood to improve the shear
>> resistance of the roof. Of course, the wall sheathing would be more
>> important to strengthen, but it is presumably not accessible.
>
> At $45/sheet? You're pretty free with the guy's money. The house has
> been standing for 50 years, so there's little benefit to be gained
> from an extra layer of sheathing. I also don't like adding weight to
> a roof unnecessarily.

Hey, events that test the lateral force resisting system are typically
high magnitude low probabilty events like earthquakes or hurricanes.
So just because it has been standing for 50 years doesn't mean that it
isn't worth strengthening _if_ the hazard is high. Hence my preface
"if you are in a high wind or seismic area."

Yours, Wayne

Posted by Harry K on April 6, 2008, 10:41 pm
>
>
> >> If you are in a high wind or seismic area, you may wish to consider
> >> going over all the T&G 1x with 1/2" plywood to improve the shear
> >> resistance of the roof. =A0Of course, the wall sheathing would be more
> >> important to strengthen, but it is presumably not accessible.
>
> > At $45/sheet? =A0You're pretty free with the guy's money. =A0The house h=
as
> > been standing for 50 years, so there's little benefit to be gained
> > from an extra layer of sheathing. =A0I also don't like adding weight to
> > a roof unnecessarily.
>
> Hey, events that test the lateral force resisting system are typically
> high magnitude low probabilty events like earthquakes or hurricanes.
> So just because it has been standing for 50 years doesn't mean that it
> isn't worth strengthening _if_ the hazard is high. =A0Hence my preface
> "if you are in a high wind or seismic area."
>
> Yours, Wayne

Well, if the winds and sheer force are great enough to rip off T&G, a
bit of ply over it ain't gonna stop it.

Harry K

Posted by Wayne Whitney on April 7, 2008, 12:09 am

> Well, if the winds and sheer force are great enough to rip off T&G,
> a bit of ply over it ain't gonna stop it.

It's not a matter of ripping off the T&G boards, it's a matter of
deforming the framing so that each rectangle formed by two joists and
two of the T&G boards becomes a non-rectangular quadrilateral. This
only requires that the T&G boards slide relative to each other.
Plywood would resist this deformation much more than the individual
boards do.

Yours, Wayne

Posted by RicodJour on April 7, 2008, 12:24 am
>
> > Well, if the winds and sheer force are great enough to rip off T&G,
> > a bit of ply over it ain't gonna stop it.
>
> It's not a matter of ripping off the T&G boards, it's a matter of
> deforming the framing so that each rectangle formed by two joists and
> two of the T&G boards becomes a non-rectangular quadrilateral. This
> only requires that the T&G boards slide relative to each other.
> Plywood would resist this deformation much more than the individual
> boards do.

It's safe to assume that the guy's framing DD's house didn't use 32"
long scrap to sheath the roof, so it's not just two _rafters_
involved, probably more like five or six or more. At the forces
required to make a, what?, 30' roof start to rack appreciably, the
whole roof would come off in a piece. Other failure modes would be
involved way before roof racking became an issue.

I understand your point about plywood adding to racking resistance,
but there's no indication in this instance - even if in a high wind
area - that the roof would benefit in any significant way from the
additional layer of sheathing. On the other hand DD's wallet would be
significantly lighter.

R

Posted by Wayne Whitney on April 7, 2008, 11:25 am

> I understand your point about plywood adding to racking resistance,
> but there's no indication in this instance - even if in a high wind
> area - that the roof would benefit in any significant way from the
> additional layer of sheathing. On the other hand DD's wallet would
> be significantly lighter.

I'm not proposing that the plywood should or shouldn't be added, or
saying that it is or isn't worth doing. I'm mainly pointing out that
reroofing provides an opportunity to improve the racking resistance of
the roof structure, and that standards for roof construction have
changed since the house was built in the 1950's. So I think it is
worth checking what the current design loads are for that area, and
then evaluating whether the strengthening is worth the cost. You are
probably right that it won't be worth it, but neither of us can say
that definitely without knowing the design seismic and wind loads for
the OP's location.

Yours, Wayne

Page 1 of 2       1 2 > last >>
Similar ThreadsPosted
Roofing question October 4, 2005, 9:25 pm
Roofing Question July 7, 2007, 9:43 am
Re: Question about roofing June 27, 2005, 7:32 am
Question about roofing June 25, 2005, 11:08 pm
roofing question March 24, 2006, 8:49 pm
re-roofing question July 1, 2006, 1:20 pm
Roofing Question May 22, 2007, 6:24 pm
Another Roofing Question May 27, 2007, 11:51 am
Roofing Question July 27, 2007, 4:33 pm
Roofing Question August 15, 2007, 12:33 pm

Contact Us | Privacy Policy

XML SitemapXML Sitemap