Hi all, first post, but long time lurker. I've just acquired a 1930's (solid wall) gable wall semi, and I intend on converting the loft space. It's a traditional cut roof, with purlins, 2 struts bearing onto the loadbearing internal walls. The plan for the space is a bedroom with en-suite. Stairs would be over the existing ground to first floor stairs, plenty of headroom there. I'll be DIY'ing it, and want to keep it as simple as possible and avoid steel beams/party wall intrusion. I'm considering going down the telebeam route as it means I can do it "piecemeal" without removing the roof, but was wondering whether if given it's a cut roof I can do it without resorting to telebeam, and just use timber to put in new floor joists, double up rafters, put some collars and ashlar stud wall. The question I have is... with either solution, how big/wide of a dormer (if any) would I realistically be able to achieve without resorting to steel beams or a steel ridge? Having a dormer would really help open up usable floor space vs. just going down the velux route. Priorities are: Not having to remove the roof, not having to hire a crane, ability to carry out the work at a slow pace (I'm not living in the house so can leave stuff half-done). Obviously will get BC to advise and sign off on final details of any proposal, but wanted to get a feel whether a dormer is realistic given the above before I do any further work. Thanks!
If you plan to cut a purlin you will be needing a steel ridge beam. You are best talking to a structural engineer to get your options fully realised
If I were you I'd have a chat with building control, no one on here can advise you one way or the other. I'd be amazed if you didn't have to put a ridge beam in to carry the thrust of the dormer, but see about doing it in Glulam NOT steel, far far easier to manoeuvre and lift. If you have a load bearing wall downstairs in the middle of the house that the struts from the purlins are resting on you may be able to span timber from wallplate to wall, and lap the joints over it, but it depends on the span and depth of joist needed. Lots of if, buts and maybe. Talk to B.C.
You do not necessarily need steels just because you've cut a purlin!! We did my daughters house some years ago: dormer some 7 feet internal with pitchedroof You do need an SE however. Find one that specialises in lofts though: many will shove a load of steels in. Better yet get someone like me who designs and engineers as simple layout changes can often have profound effects on the structure. NOT AN OFFER: TOO BUSY Are you sure the front to rear walls are load bearing? Wouldn't usually be.
Thanks all for the responses. I've just been up the loft with a measuring tape again and reckon I can get away without a dormer (i.e. just velux windows!). Would still want to remove the purlins, so will speak to BC and find a local engineer. Am I also wrong in my assumption that I can't remove the purlins and replace with a load-bearing dwarf stud walls and ceiling collars as part of a telebeam conversion, which in my simple head ends up the same structure whether you start with fink trusses or my cut rafters? (see attachment) Re internal walls, apologies, probably wrong terminology, I don't know if they're "load bearing" nor not, but they're solid brick (half brick thick) from ground floor all the way up to eaves level. Thanks
Telebeams are great and the people there are really helpful, but with a central load bearing wall it's a simple timber job. Walls under rafters to replace purlin onto floor joists and away you go. Personally I would have a dormer: you get so much extra space for a comparatively small extra cost
If you have struts supporting the purlins and travelling down to a spreader plaster sat on top of an internal brick wall, it's safe to assume the wall is contributing to supporting the roof, I.e. load bearing. Look up the thread 'Telebeam installation', on this very own forum, under the sub title 'Project Photos', a member on here called Jitender is undertaking the loft conversion, and all associated work with it, it's a cracking read and cracking job, it may be of use to you.
Had LABC out on Saturday (my god they're a helpful bunch!) - looked in the loft and my plan for timbers, said it was very straightforward. Double up rafters with 6x2, lay 8x2's for new floor on central spine wall and wall plates, and 4x2s for dwarf wall to remove purlins. Job jobbed. Since then I had a think about it and three things sprung to mind, but probably me overthinking: 1) The current loft has a big 8x2 on end nailed across to the tops of approx half the ceiling joists at mid span in the rooms, presumably to stop them sagging. This is going to go when I put new floor joists in, but given new joists won't be tied into the old ceiling joists (I was advised to not join them), is there any way to stop the 4x2 ceiling joists from sagging? Alternatively, how much of a problem is it to tie the new 8x2 joists to the old ones? The ceilings below will need a skim over regardless of the loft conversion. 2) I can't double up the existing rafters with 6x2 until I remove the purlins (for obvious reasons), so is the process to put new floor joists in, then the dwarf wall to support the original rafters, then remove the purlins before doubling up the rafters? Is there not a risk that the rafters will sag before I get a chance to double them up once purlins gone? The dwarf wall will be approx 50cm further down the roof slope from current purlins. 3) As far as I can see there are no diagonals or anything else to constrain the rafters in shear once all this is done... Am I overthinking it, and the two brick gable walls + all the plasterboard once fixed will do that adequately? Cheers!
In short, 1. I disagree, I've always tied old joists to new via large screws/bolts if alongside, or fixed builders band strapping to tie the structure together, never had any problems off building inspector each time. Perhaps in your case you could fix builders band off the sole plates of your dwarf walls supporting your rafters, and tie to the original ceiling joists underneath, breaking up the span into three sections. 2. Joists first, then notch two and a half inches out of the top of the purlins alongside each existing rafter (assuming they're 4x2), then slide up the new 6x2 rafters, push tight to the roof battens and fix to existing rafters. Then build your dwarf walls underneath, then remove purlins. 3. No you're not overthinking, it's a valid question, but no need to worry, you're gables and newly built dwarf walls will be structurally sound, any stud walls you build will support and lock in the roof structure, and as you say, the plasterboard fixed to the rafters will be acting as a brace in its own right. Once all separate components are tied together strength won't be an issue.
If you are replacing the purlin with a purlin wall, then the rafter support isn't affected and you shouldn't need to change them: sounds like some confusion here.
Thanks all Jord, very comprehensive, much appreciated, esp. Point 2 - makes a lot of sense. Am I right in that I effectively put a bolt (with timber connectors) through all three bits of wood where the doubled up rafters join the dwarf studs, or is it best to fishmouth or just rest the original rafters on the stud wall? Just seems odd for some reason to have none of them bearing directly on one another! Stevie, the "purlin wall" will be further out and not directly under the current purlins, so the rafters will be over a wider span than currently between ridge and purlin. Kool, I'll try and get some pictures up, if for no reason other than someone else might have a similar set up and this could be a useful build diary! Cheers
I'm not 100% on what you mean, when you build a dwarf or ashlar wall underneath the rafters, you fix a sole plate to the floor joists, a head plate to the rafters(doubled up is best, as you don't explicitly have to have the studs under each rafter then, good for eaves cupboards location), and studs in between. You don't have to bolt the studs to the rafters, to be honest you could only do so if you leave out the head plate of the dwarf wall and I wouldn't recommend that, as each rafter is completely reliant on the stud beneath then, whereas with the head plate the weight is distributed throughout the wall. Hope some of that makes sense.
That's exactly what I was asking, thanks Jord (I've seen photos of studs bolted to rafters, with no head plate). What you're saying makes perfect sense. doubled up 4x2 going across the rafters suitable head plate? Would the headplate sit level (therefore with an angle to the rafters in which case, fishmouth rafters?), or at an angle to be flat to the rafters, with the studs being cut at an angle at the top to rest on the headplate?
Double head and double sole plate, fix sole plate first to a straight line, plumb up and fix head plates flat to the underside of rafters, then cut angled studs to fit between plates. One thing to watch out for, is as you are fitting the head plates on an angle make sure you plumb the walls off the furthest projecting part of the head plates(the corner), NOT just plumb up off the sole plates, snap a chalk line and fix your head plates edge to that, your wall will be out of plumb if you do that. Difficult to explain in writing, but I would screw your head plates rather than nail, if you have to move them to suit the sole plates then it's no problem.
D'oh, "fishmouthing" from metal tube fabrication head fart! I obviously meant birdsmouth... Thanks for tip re plumbing walls, got it!
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