Gaf Posted September 15 Share Posted September 15 Curious to get opinions about the completed roof in two areas of our build versus what was shown on the construction drawings. Query comes from the carpenter and builder both mentioning the steel specified by the architect wasn't even needed and we could actually have it removed if we wanted. Am I right that the construction drawings had the steel beam as the ridge with the rafters then 'attached' to this? Whereas the carpenter/builder have put in a wooden ridge and placed the steel beam below this, with the steel beam now creating the need for the joists that weren't on the construction drawings? Link to comment Share on other sites More sharing options...
Alan Ambrose Posted September 15 Share Posted September 15 Yeah, reckon so - the only reason for the RSJ being there is to support a load. Are you sure that it's not and are you sure it was the architect that specified rather than an SE? Seems to be a common: this 'paper pushers don't know what they're doing, we, the builders have done it all before and are far smarter' thing. Apart from figuring out what really is happening load-wise and that there's nothing untoward going on, I wouldn't sweat it - unless there's a major problem, it's not going to be changed now, is it? You can always call the builder's bluff by asking for an as-built drawing and corresponding load calcs. And/or get the architect/SE in to check and confirm whether the as-built is good or bad. 1 Link to comment Share on other sites More sharing options...
ProDave Posted September 15 Share Posted September 15 That steel is a ridge beam supporting the weight of the roof. If you took it away, then the weight of the roof would be supported on the timber rafters which would transfer the load to the walls, but in doing so would push outwards and the rood would spread. Those ties at the top are not enough to stop the roof spreading. 4 Link to comment Share on other sites More sharing options...
Mike Posted September 15 Share Posted September 15 (edited) Rafters need something to stop them splaying apart, normally a horizontal timber tie. An alternative would be to securely fix them at the ridge to some kind of beam, and that beam would need to support 50% of the weight of the roof. To remove the beam and the ties, the foot of the beams would need to be fixed so they couldn't move, and the wall would need to be strong enough to withstand the sideways load - for example by casting a concrete ring beam. In the drawing above, I can't see how the timbers could be properly secured as drawn, so the carpenter's solution is a good one. To dispense with the RSJ in that situation, the horizontal ties would need designing by a SE. Edited September 15 by Mike 1 Link to comment Share on other sites More sharing options...
ProDave Posted September 15 Share Posted September 15 At least the designer of my house specified what brackets and even what screws / nails to use and how to fix the rafters to the ridge beam. Link to comment Share on other sites More sharing options...
Mr Blobby Posted September 15 Share Posted September 15 (edited) I think your roofers have done you a favour by installing a timber above the steel and attaching the rafters to that timber. In doing so they have brought the steel further inside into the warm side of the loft instead of being a cold bridge resting on the inner leaf. I see no airtight membrane included in your roof buildup. Also, given this looks like a hybrid warm roof with 50/50 insulation on top / beneath the rafters, then have you done a condensation analysis? Edited September 15 by Mr Blobby 1 Link to comment Share on other sites More sharing options...
saveasteading Posted September 15 Share Posted September 15 The steel is necessary. Takes the load to the end walls. We used laminated timbers instead but the effect is the same. Without it you would need lots of diagonal truss bracing and would have an attic, not a room. Diagonal truss bracing stops the rafters from both bending and thrusting out. And relax. 2 Link to comment Share on other sites More sharing options...
ETC Posted September 15 Share Posted September 15 8 hours ago, Gaf said: Query comes from the carpenter and builder both mentioning the steel specified by the architect wasn't even needed and we could actually have it removed if we wanted. Might be the time to get yourself a new builder and joiner - sorry carpenter! 1 Link to comment Share on other sites More sharing options...
Oz07 Posted September 15 Share Posted September 15 Maybe you need a better connection detail to help them out. Your drawing looks to require the rafters to connect to the face of the steel but for it to still work like a ridge beam you would then need timber inside the flanges with hangers cut into the rafters. Or rafters cut into flanges and blocking between. It needs a zoomed in detail. 1 Link to comment Share on other sites More sharing options...
torre Posted September 16 Share Posted September 16 Why didn't your builder ask why there's a steel beam that's 'not needed' before building a roof around it? Agree with others the steel ridge beam is to hold your roof up, stop spread. This Robin de Jongh video explains exactly why the ridge beam works and why those collar ties are not enough, well worth 6 minutes watching. Double check that the timber above (which the rafter are fixed to) sits directly onto the steel itself, in which case the beam will do its job. If not then the timber below won't be enough to stop the roof spreading later. From the membrane on the rafters it doesn't look like the builder's following the description of the roof build up so you should clarify what they're intending - maybe they are trying to avoid the hybrid roof? 1 Link to comment Share on other sites More sharing options...
Gaf Posted September 16 Author Share Posted September 16 Cheers for all the replies. There were a lot of conversations on site that day and I got my wires crossed on this. We have two rooms with vaulted ceilings, one is 3.2m2 the other 4.3m2 (the photo). The joiner/carpenter said the steel wasn't needed on the 3.2m2 room whilst the builder just said in his experience the steel specified on the drawings for both rooms was overkill for the roof size, that much smaller (and cheaper) steel beams could have been specified but he didn't suggest the steel wasn't needed. Can see the consensus is the steel beam is absolutely needed. Seems the beam wasn't drawn very well on the construction drawings as it would have been difficult to have the rafters fitting into it, plus the steel beam would have been a thermal bridge. @torre That video was really helpful, cheers. Was reassuring to see the steel beam was the recommended approach. Will get up and check the wooden ridge is sitting on the beam - would it be expected to look something like the attached? Link to comment Share on other sites More sharing options...
saveasteading Posted September 17 Share Posted September 17 4 hours ago, Gaf said: steel beam is absolutely needed At the moment it is weighing down the trusses. So get the gable wall built asap. Presumably a padstone will be under the steel, and somehow it will need to be packed hard up under the steel. slates hammered in is the usual . 1 Link to comment Share on other sites More sharing options...
Gaf Posted September 17 Author Share Posted September 17 That’s just a photo I found online. Link to comment Share on other sites More sharing options...
saveasteading Posted September 17 Share Posted September 17 1 hour ago, Gaf said: photo I found online Ok. Don't ever assume i (most on here?) have reador remembered the whole discussion. Is yours on padstones? Link to comment Share on other sites More sharing options...
Gaf Posted September 17 Author Share Posted September 17 Yes it’s on padstones. Link to comment Share on other sites More sharing options...
Gaf Posted September 17 Author Share Posted September 17 (edited) Close up is on the 4.3m2 beam. How does she look? Ground level shot is the smaller room (couldnt get access to the scaffolding on that side). Edited September 17 by Gaf Link to comment Share on other sites More sharing options...
Temp Posted September 17 Share Posted September 17 The weight of a roof tends to push the walls outwards. The main way of stopping this on a two storey house is to use joists to tie the bottom of the rafters together to form triangles. This design only needs a ridge board not a beam. Problem is you can't do this with a "room in the roof"/ 1.5 storey house because the joists would get in the way. A common alternative is to "hang" the rafters from a steel ridge beam and that's what your architect did. The ends of the beam are supported on pad stones in gable walls or chimneys which carry the load down to the ground. I believe the rafters should normally be strapped together above the ridge beam with metal straps. 3 Link to comment Share on other sites More sharing options...
Gaf Posted September 17 Author Share Posted September 17 38 minutes ago, Temp said: The weight of a roof tends to push the walls outwards. The main way of stopping this on a two storey house is to use joists to tie the bottom of the rafters together to form triangles. This design only needs a ridge board not a beam. Problem is you can't do this with a "room in the roof"/ 1.5 storey house because the joists would get in the way. A common alternative is to "hang" the rafters from a steel ridge beam and that's what your architect did. The ends of the beam are supported on pad stones in gable walls or chimneys which carry the load down to the ground. I believe the rafters should normally be strapped together above the ridge beam with metal straps. Ah that makes a lot of sense - I hadn’t understood it as the roof effectively hanging on the beam. Only things I’m left wondering about are the metal straps you mentioned (not so sure they were used) and the pieces of slate used between the beam and the pad stones. The slate shims look a bit rough to me but not sure if that’s typically how it’s done… Link to comment Share on other sites More sharing options...
saveasteading Posted September 18 Share Posted September 18 1 hour ago, Gaf said: The slate shims look a bit rough to me but not sure if that’s typically how it’s done… yes that is rough. the principle is that the beam needs to be levelled, if the padstone has been placed too low, and that ALL the steel should be in contact. Thick mortar would shrink/crack. So slate is used WITH mortar. This isn't good. The slates may crack but then stability will occur. At least they must squeeze in what mortar they can to help spread the load and dress around that mess. Could be worse. They might have packed with wood or plastic shims 1 Link to comment Share on other sites More sharing options...
torre Posted September 18 Share Posted September 18 9 hours ago, Gaf said: shot is the smaller room (couldnt get access to the scaffolding on that side In your position, I'd definitely pay for your SE to come out and inspect before you start putting the roof coverings on. You'd want that to include the larger room too, even if it means taking down a couple of blocks to see better. Did they slide the beam in after rather than seating it and building onto? It's not level, not clear it's actually bearing the weight above yet. As the timbers aren't fixed to the beam, the rafters aren't either, only an SE can tell you how much that affects resistance to racking forces (using words I barely understand at this point!) A couple of hours of an SE's time will be a small price for the reassurance you'll get, or give you a clear scope of any corrective work needed - any fix will only get a lot more expensive later. Link to comment Share on other sites More sharing options...
Gaf Posted September 18 Author Share Posted September 18 (edited) @saveasteading Not sure how difficult it would be but Im tempted to ask them to redo those slate shims with neater pieces. @torre Yeah I was thinking it didn't look level and didn’t look like the timber was actually sitting on the steel (not sure if that’s partly because of a slight bend in the timber at that end point). The steel was put in place before any roof work was done. They must have planned to raise the steel up with the shims but it looks like a messy job of using the shims. The architect specified the steel work as he said the required steel work in our house wasn't complex so he was qualified so sign off on it. Said an SE wasn’t required due ti the simple nature of the structure. We have a chartered building surveyor signing off on each stage of the build so Ill get onto him and ask if he’s inspected this yet. Edited September 18 by Gaf Link to comment Share on other sites More sharing options...
Dave Jones Posted September 18 Share Posted September 18 6 hours ago, saveasteading said: yes that is rough. the principle is that the beam needs to be levelled, if the padstone has been placed too low, and that ALL the steel should be in contact. Thick mortar would shrink/crack. So slate is used WITH mortar. This isn't good. The slates may crack but then stability will occur. At least they must squeeze in what mortar they can to help spread the load and dress around that mess. Could be worse. They might have packed with wood or plastic shims perfectly normal to use slate as a packer, less common to see though as most have access to a laser these days to get it right. Not all steels are bang straight though either! Link to comment Share on other sites More sharing options...
Gaf Posted September 18 Author Share Posted September 18 11 minutes ago, Dave Jones said: perfectly normal to use slate as a packer, less common to see though as most have access to a laser these days to get it right. Not all steels are bang straight though either! Yeah I found lots of posts with slate recommended over other materials as it already has massive compression strength. Would you expect the slate to look a little neater than was done though? Link to comment Share on other sites More sharing options...
torre Posted September 18 Share Posted September 18 2 hours ago, Gaf said: The architect specified the steel work as he said the required steel work in our house wasn't complex so he was qualified so sign off on it. In that case, why not send him these pictures and ask if he's happy it's constructed as designed? Never hurts to get that sort of thing in writing. If the ridge beam is working as designed, you should be able to remove those collar ties and get some of that vaulted ceiling height back. See how happy your builder is about that 1 Link to comment Share on other sites More sharing options...
Gaf Posted September 18 Author Share Posted September 18 1 hour ago, torre said: In that case, why not send him these pictures and ask if he's happy it's constructed as designed? Never hurts to get that sort of thing in writing. If the ridge beam is working as designed, you should be able to remove those collar ties and get some of that vaulted ceiling height back. See how happy your builder is about that Architect has been good with minor queries so far related to certain detailing not included on the drawings (e.g. he specified ridge heights and roof angles but not wall plate height as he said that’s calculated on site). He’s kept a boundary on signing off on anything on site though as we didn’t hire him to certify anything and has (I think very fairly) pushed back on this being our certifier’s job now (building surveyor). Joiner said the collar ties have to stay because they’re needed for the worked needed for the insulation and air tightness. No idea myself on that… Link to comment Share on other sites More sharing options...
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