Loft conversion/Cut Purlin

RMIM · 4 Aug 2008

Hi Everyone,

I have just been to my mate’s house and he has got a builder to do his loft conversion.

It seems that he has just cut a purlin and offered no other support (im not sure if he finished yet) to accommodate a window. See pic

What is the correct way to do this?

If I were doing it, and the purlin had to stay, I would just put 2 windows - one above and one below the purlin, rather than 1 big window to avoid cutting the purlin.

Any advice appreciated.

Untitled

RMIM
4 Aug 2008
1

^woody^ · 4 Aug 2008

Ye-harrrrrrrrrrrrrrrr.

What do the plans say, and what about the BCO? And where are the double rafters?

It doesn't look much of a purlin though, was it doing anything, I wonder?

Best advice, is the get the builder to open the window to inspect the external lead, then grab his ankles and throw him out.

noseall · 4 Aug 2008

well, if he has butchered the purlin, what are the chances that he's beefed up the floor joists?

this builder needs exposing...........

RMIM · 4 Aug 2008

No the floor joist have not been beefed up (yet) - and I dont think he was going to. But there seems to be a joist higher than the rest and it does not seem a good idea to remove it. So I think he will have to make the floor level with that one, which will result in beefing up the other joists.

I dont think guy knows what he is doing.

I dont think he has seen BC. How will he go about seeing BC now that he has hacked his loft, making it possibly unsafe, without getting in trouble?

^woody^ · 5 Aug 2008

If he is doing it properly, then he will need b/regs approval and your mate will have submitted an application.

If he is doing this without an application, then your mate is relying on the builder having some sort of clue what he his doing. However, it seems that your builder is out of clues, and your mate out of luck

AndersonC · 5 Aug 2008

^woody^ said:
Best advice, is the get the builder to open the window to inspect the external lead, then grab his ankles and throw him out.

Cheered me up mate!!

!!

DCS · 5 Aug 2008

Should not collapse the roof but this is an absoloute no-no!
Stop the job now, do not pay the builder and bring in a structural engineer - this is a bodge job and needs sorting - seems like he should have got you to do the job!

noseall · 5 Aug 2008

^woody^ said:
If he is doing this without an application, then your mate is relying on the builder having some sort of clue what he his doing. However, it seems that your builder is out of clues, and your mate out of luck

priceless.

RMIM · 5 Aug 2008

Keep the jokes coming guys but try to add some building advice in them too.

What would BC have told him to do - or is it not possible for anyone to say from that picture I gave? Would some dimensions help? I would like to get as much info as I can before the builder comes back. That way I could possibly steer him in the right direction.

Thanks.

Shytalkz · 5 Aug 2008

How shall I compare thy roof to a complete lash up? Let me count the ways...

Purlin: undersized by current standards, but, before being cut, seemed to have performed ok, without sagging overly, either into the roofspace, or down the slope, no doubt aided by the relative steepness of the pitch. Now that it has been cut through, it is doing precisely.....nada, other than hanging off the rafters. Expect future sagging of the roof structure and outward spread at the eaves.

Velux: the opening has been trimmed out, but the rafters either side have not been doubled up. Expect future additional sagging of the roof to occur around the opening.

Wallplate: this is above ceiling level, so there is no triangulation of forces to restrain the rafter feet; however, the original purlin gave a degree of restraint to the roof and stopped this ^ becoming this --. Now the purlin is cut, the only thing, so far, stopping the roof spreading is the friction between the top of the plate and the wall, unless there is a lean-to roof the other side, which we can't see on the photo. Expect this at some point to slip towards the outside and the roof to sag some more.

Joists - going by what we can see, presumably the existing joists have merely been overboarded, rather than new, adequately-sized ones installed, designed to take the required occupancy loading, which is 6 times that of a loft space. Expect sagging of the joists, cracking of the ceilings underneath.

Are you getting worried by what he's done yet? You should be....

gangman · 5 Aug 2008

The first thing I'd ask, has the purlin been left in on the drawings. If it has there should be a detail to explain what was wanted around the window opening.
If there's no detail then whoever done the drawings has not done their job properly. If there is a detail then the builder should have followed it.

Detail or no detail, what he's done does not look right, bearing in mind we're only seeing one photo. Any one experienced in roof structures will know cutting out timbers alters the structure somewhere. You don't really find timbers in a roof that aren't supporting something.

Personally I would take out the purlin, it's not a good design having that sticking out of the ceiling. I think it can look a bit of a cheap job leaving the purlins showing. I would have made sure the roof was properly braced before taking out the purlin, and then taken it out in sections.

On the face of it this guy isn't clued up on loft work, if he does something major like this, what about the little important things that don't get noticed. The building industry has been good for the last few years and suddenly every one and his mate have become builders. I hope this guy has proper insurance, and I don't mean one for £200 a year either.

Shytalkz · 5 Aug 2008

Gangman, the existing rafters are not suddenly and miraculously going to span twice the distance that they originally did, with a heavier load on them (p'board and insulation) with the purlin removed, so, clearly, some kind of strengthening would be required to the whole slope and not just where the velux is trimmed out. Even with the purlin left in, the roof would need strengthening, as the purlin, through being cut, is now entirely redundant.

gangman · 5 Aug 2008

Shy
Give me some credit, please. On most of the lofts I've done if the purlin can't be hidden with a wall or something, they are normally taken out. One architect I worked with in London would only have 600mm upstands and no purlins left in unless hidden.
On these lofts we'd put in new rafters along side the existing, costs more but it wouldn't look like a loft. As you point out, the extra loding on the rafters should be considered. Seen a few lofts that have sagged where they relied on just the existing rafters.

AndersonC · 5 Aug 2008

RMIM said:
What would BC have told him to do ....

Work for Mcdonalds.

Relevant building advice would be to ensure he only serves burgers.

Shytalkz · 5 Aug 2008

Not having a pop Gang, honest!

It's nigh on impossible to justify existing purlins to current standards, particularly where they are on the slope, as they bend in two directions, so one way of getting the roof to work is spanning the rafters from plate to ridge, which invariably, as you say involves doubling up and possibly trebles where trimming out velux.

This particular one is made even worse by the lack of a tie to the rafter feet at plate level. The bloke who is doing this clearly does not have a 'kin clue.

AndyC got it right in one...

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Loft conversion/Cut Purlin

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