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I am selling my house, our original survey when we purchased said the roof would need strengthening due to the original slate being replaced with concrete tiles quite some time ago.
Nothing to worry about, we were told, easy to do DIY. Seeing as the ridge is straight and no sign of sagging we just left it for five years knowing that most of the other houses are probably in exactly the same position, but now we are selling, what would be involved just to keep it from cropping up again in the buyers survey?
Its a mid terrace house, quite a small roof.
The ridge is just under 12' long. Rafters are 4x2, joists are 4x2 and approx 23' long, approx 15" c2c, purlin on one side is 4x3 and the other is 6x2, I think the bigger one is a replacement. The purlins are approx 4' from the joists.
Am I correct in thinking I just need to add some uprights to support the purlins mid span? If so, what size should I be looking at and I guess I would need a span across the ceiling joists to prevent the ceiling downstairs from sagging?
Or, on the other hand, would any further investigation by someone independent just say it was fine (but that would probably cost more than an afternoon playing with some bits of wood)
Thanks 🙂 I did post this on a DIY forum but got no response!
You called?
You need 2 or 3 pairs of strutts made of 4x2 that ideally want to come down to a supporting wall.
Both your purlins are quite small TBH
Not the best pic, i'll see if i can find better but
http://toolboxes.flexiblelearning.net.au/demosites/series10/10_01/content/bcgbc4010a/12_roof_systems/02_conventional_roof_framing/page_006.htm
5th pic down you'll see where the 4x2 is cut around the purlin
http://wiki.diyfaq.org.uk/index.php?title=Roof_construction
Hope these help
Thanks for your help. So I would need two struts per purlin minimum. Its a two up, two down house with a stairs up the middle.
Onto a structural wall may be difficult, one side of the stairwell is brick to the 1st flr, then studwork/plaster and lathe to the ceiling, so I assume this would be structural. But to get the struts over this they would need to be a fairly shallow angle, one of your links (the .au one) says a maximum angle of 35 degrees from vertical but I think mine would need to be nearer 60 degrees. Vertical would put the load straight over the middle of the ceiling.
The other side of the stairs is open, so the bedroom wall is sitting on a joist than spans across the house. So I guess I could potentially do more harm than good by putting struts over this wall. Again the angle would be similar, 60 degrees or so.
Maybe it is best just to leave it well alone, and if it crops up I will just tell the buyers it just needs a couple of struts per side.
With purlins that small 3 pairs really. You can space them around the stairwell, your right you dont want to go over that.
What you do to get them at a nice angle and near the wall is to first fix a piece of 4x2 around 4' on to the ceiling joists in the centre of the span and have the strut's coming down to the ends of that (if that makes sense)
You can just make it out here http://diydata.com/general_building/roof_construction/roof_construction.php
I've just tried drawing a sketch but it doesn't help...
So this 4' bit of wood, are you saying it should:
Run across the joists over the bedroom ceiling below (in the same direction as the purlin), with a strut either end, and it would spread the weight of the roof over the ceiling. (not over a load bearing wall)
Or:
Run the 4' wood in line with the appropriate joist, so one end is over the supported wall, and the strut would sit on the other end over the bedroom ceiling?
From that last diagram, my roof doesn't have any hangers or a ridge collar. Before your last post, this is what the struts would look like if they went to the load bearing wall. At this angle I don't think they would actually be doing anything else apart from weighing the purlins down further 🙂
[url= http://farm9.staticflickr.com/8036/8065856104_6c0dba1e87.jp g" target="_blank">
Could you double up the Purlins? This has been done in my roof. I found the struts were hanging loose as the ceilings had sagged more than the roof so removed them to make more usable space.
When I insulated the roof space I put insulation between the rafters then ran a set of rafters (in fact they act as small purlins) perpendicular to the original ones to hold the insulation in place, more insulation went in before boards. The result is a framework which is a lot stronger and flatter than before.
Replacing the tiles with solar panels on the south side cut the weight.
It still looks like a canadian tent but at least a tightly pitched one.
I'll draw something tonight but yes the 2nd way.
Timber goes in line with ceiling joists not the purlin.
In your drawing the bottom of the strut's meet, they want to be 4' or so
apart and thats where the timber goes.
Struts want to be bird mouthed into the purlin and the timber, cut ever so slightly
over-sized so they are tight
Id put a steel plate front and back, pre drilled, line em up then bolt thro. I wouldn't want to load any extra weight onto ceiling joists, and at the angles you are talking they won't do owt anyway.
Ah it suddenly makes sense...the timber bridges the supporting wall, and each end supports a strut, one too each purlin. So it would be a cantilever (or whatever the word is) to avoid loading the ceilings.
I can see this being a whole lot easier once the loft is empty (the floor is boarded) so I may do it if the buyer thinks its a deal breaker rather than doing it just in case. The last thing I'd want is the surveyor finding it half done!
the help is much appreciated, thanks!
As I understand it I need to do this:
[url= http://farm9.staticflickr.com/8314/8066881920_f562e0d764.jp g" target="_blank">
Does it matter that the supporting wall is not central to the new timber?
That's it, you'll have to test a bit before cutting, the 4' bit was a bit of a guess (bout 20 years since i last had to actually do it)
You don't want it too long otherwise the ceiling will be taking too much load. Your ceiling joists will prob not be in one length but 2 lengths that cross over each other at the supporting wall, you want to nail it centurally over the 2
Where the strut meets purlin and timber it will have to be notched (birdmouthed in), pic coming of that
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Thanks. So just nail it to the joists over the supporting wall. What about the ends near the strut, are they fixed to the joists here as well or would that cause the load to shift onto the joists more?
And can I use those spikey plates either side of the wood instead of nails?
Sorry for all the Q's but you've been a great help!
Nail it evenly all the way along, 4" galvo nails, the strut also needs to be spiked in with the same at the purlin and timber but take care not to split the wood
Hehe...last questions...
It sits on top of the joist, not alongside, right? Skew nail it to existing joist from both sides I guess.
Where the strut meets purlin, pic 5 in an earlier link, the strut is notched around the purlin? (the purlin isn't notched at all)
Thanks
Yep on top, nail every foot or so.
Yep has to be birdmouthed into the purlin, not the purlin itself
that would weaken it