Replacing a purlin
Jenny Brett
prefer to do it from "the inside", ie. not take the roof off to do it.
All the internal walls and ceilings will be removed at some point, so
hopefully that would be possible.
Is it possible? And if so, how could we go about it?
Jenny
Jan Wysocki
>
> * Newsgroups: uk.d-i-y
> * From: Jenny Brett <jen...@madasafish.com>
> * Subject: Replacing a purlin
> * Date: Tue, 13 Mar 2001 22:44:16 +0000
> * Organization: Posted via Supernews, http://www.supernews.com
>
> ------------------------------------------------------------------------
> [Previous] [Next] [Reply] [Index] [Home] [Find]
> Newsgate.co.uk is maintained online by Dario Centofanti
enny
Judging from the purlins in my loft, one of my purlins had a
rotted end some time in the past. Only the rotted end has been replaced,
essentially by cutting out the affected timber and inserting a new timber with
a scarf (diagonal), unglued joint. To do this it would have been necessary
to support the purlin close to the cut and support the roof timbers
immediately above
and below the part that was being cut out.
All the force on a purlin is perpendicular to the angle of the roof:
Just make sure that your supports are also perpendicular to the angle of
the roof - this means that they point in the same direction as the inner
face of the purlin.
--
Jan
with an ongoing loft project.
--
Posted from relay1.bt.net [194.72.6.100]
via Mailgate.ORG Server - http://www.Mailgate.ORG
Gerald Foster
which shares the load of the roof including the tiles (which probably
accounts for most of the load). If you are planning to remove it you
would need to either remove the load (the tiles) or provide some
temporary support while you are replacing the purlin.
If you dont want to remove the tiles I would use a (or several)
structural support post to take the load and jack up the roof, but only
to take the load. The purlin can be removed through a exterior gable end
(if there is one) by removing the outer skin of bricks. the new perlin
can be slid into place in the same way.
Personally I would only replace as much as required and save a load of
agro...
Gerald Foster
Jenny Brett
Gerald Foster wrote:
[Snip lots of good stuff]
> Personally I would only replace as much as required and save a load of
> agro...
>
I suggested supporting the roof, cutting off the rotten end and
replacing it with a new bit of wood diagonally cut and got such a
sucking of teeth from my other half I wondered if he'd been a builder in
a previous life!
If we were to do that, which way should the diagonal slant? How do we
fix the old wood to the new wood? What assurances can I give my other
half that this is a structurally sound way of doing this repair?!
Jenny
Gerald Foster
have to replace the whole thing. Some are supported at intervalls along
its length and you can scarf the purlin at that point. You could
introduce a new support joist (perpendicular to the roof angle) at the
join but you would need a strong joist underneath (at ceiling level) to
carry the load.
Gerald Foster
Stuart Grant
> If we were to do that, which way should the diagonal slant?
through it at both narrow ends.
> How do we
> fix the old wood to the new wood?
or 5 screws per end.
> What assurances can I give my other
> half that this is a structurally sound way of doing this repair?!
hasn't actually fallen down yet has it? The repair has to be stronger
than the rotten end.
You could get a short length of similar section timber and make a
similar joint, the diagonal should be at least twice the length of the
larger dimension, or about 25degrees to the length. Then give him a
sledge hammer and ask him to test it. If you've done a proper job it'll
break somewhere else before the joint fails.
Stuart Grant
Mark Roberts
<jen...@madasafish.com> writes
Older roofs with no ties (doubling as ceiling joists in newer houses)
running between wall plates depend on the purlins to prevent the rafters
pushing the top of the walls out (amongst other things) . You can see a
curve in most old purlins to this effect. Where the purlins are
supported at the gable walls the force is transmitted to the masonry at
an angle somewhere between vertical and inline with the rafters. You'd
have to find the weight of the roof structure to calculate this.
The upshot of all the above moiddering is that the repair has to be
strong. We have used halved joints in the past with large bolts and
spiked connectors. This depends on the existing purlin being sound.
A better more secure repair are 'fitch' plates; 2 6mm steel plates 2/3
the depth of the purlin fitted to each side and bolted together through
the wood with 2 runs of bolts. The plates should overlap the existing
and new wood by approximately 0.5 meters. Its ugly but it does work, it
can be proved with calculations from a structural engineer; whose advice
is essential before you follow the above advice as roof load, existing
purlin condition, purlin material and type of masonry all play a role.
To actually fit the new section; jack up the purlin with an acrow prop
on a large plank. If the house is 2 storey then support the floor the
prop is on from below with another prop. Tie the 2 purlins together with
a wire rope and a turn buckle to prevent the roof going anywhere
sideways (seen that). Remove enough masonry from the wall to facilitate
removing the sawn off purlin section from the wall. Saw the rotten
section off. Use a pad saw to saw through any nails holding the rafters
onto the purlin. Be surprised how heavy a wet rotten purlin end is.
Insert new purlin end and apply fitch plates firmly. Re build masonry
and leave props in place for a few days.
Remove props and wish you'd got a good builder to do it.
:)
--
Mark
Jenny Brett
Many thanks for that.
Jenny
Stuart Noble
Jenny Brett wrote in message <3AB06B6E...@madasafish.com>...
>> > How do we
>> > fix the old wood to the new wood?
save having to do any kind of joint. Difficult enough sawing a square end
with the tiles in the way.
Gerald Foster
be reluctant to rely on glue.....
Gerald