Annker

Thanks for the response, apologies to all for the late reply! To @Simplysimon and @Gus Potter If you had told me a few months ago can existing joists be strengthen by gluing and screwing addition joists on edge I would have ?. However I have recently discovered this can work in structural terms at least. I watched an analysis of the performance of this connection here https://www.youtube.com/watch?v=rgsdJ4zF8DA&t=148s, Fischer have even developed software to model the performance https://www.fischer.co.uk/en-gb/service/design-software-fixperience/wood-fix. Now this connection may perform structurally, however given the likelihood that the existing joisting may have crept and bowed down any timber fixed to those existing bowed joist will assume a similarly bowed top plane; and thence an uneven floor level. I imagine that may not be an issue if the loft space is converted solely for storage but may be unacceptable if the loft space is converted for habitation and associated floor coverings. You could over size the additional planted on timber and plane down to a level datum but that would be a painful job and best avoided if at all possible. And as as @Gus Potter highlighted with this method there is less opportunity to decouple the new floor above from the old ceiling below and thus reduce acoustic transfer and risk of cracked ceiling below. To @Temp and @Gus Potter yes you could sister in the C-sections and that would be my preference. To isolate form the exisitng plastered ceiling 1" packing pieces tacked on to the wallplates at either end and any rising stud walls from below where necessary. But I would also try to isolate the C-sections completely from the existing joist, The C-sections would be suitable sized to span independently without any connection to the existing joist and in the absence of joist bridging a structural subfloor could provide support to ensure the C-sections remain upright on edge. However after thinking out how the C-sections would be practically installed I think biggest challenge (and probably the reason that they are seldom use in loft conversion) is as @Gus Potter mentioned; existing joist bridging's, ceiling joist runners and existing services will likely be laid at or on existing joist level. I imagine it would be extremely difficult to remove those timber members for the ceiling joist without cracking the underlaying ceiling and even if you did managed to remove them what then replaces them to provide the support to the existing ceiling joist, will there even be scope to install anything given that C-sections will also be introduced into the void space. And then rerouting any services that are similarly within the ceiling joist void space will also need to be done. So to answer the my initial question! WRT loft conversation: at first impression, construction of an entirely new floor structure and the installation of cumbersome RSJs to provide support for those joists seems much more work than running in C-section joists however being constructed above and entirely independent of the existing ceiling joist arrangement it avoids the awkwardness of working in and around that existing structure.

I dont know, personally I cant see that being the reason; or if it is it should not be to my mind anyway! Effectively beefing up the existing arrangement with (numerous and less loaded) galvanised section is far less of a technical challenge than specifying where much fewer and greater loaded UC/UB should be positioned. I can imagine there may be some situations where the additional loading cannot be carried by the existing load bearing walls (typical those are the front and rear walls) and therefore transverse RSJs must be introduced to transfer the loading on the party and/or gable end walls

I will be starting a loft conversion project in a few months and considering if I can avoid using RSJs to provide support to new loft floor. Nearly all loft conversion project video I've watched on youtube seem to use ridiculous sized RSJ sections which seem to be way OTT for the loads involved. So I am try to figure out why light gauge galvanised steel joists are not used more often in traditional cut roofs loft conversion; it seems to be more popular option where the existing roof is a truss roof. To me there seems to be a lot of benefits in using galvanised joists instead of RSJ: Maximised loft floor to ceiling height as the galvanised joists can more or less be set within the existing floor/joist build up/void space Less manual handling Do not need to be pocketed into party walls; hence lessening the chance of cracking the walls of neighbouring properties I assume that the price must be the issue but at a glance I cant see there being a massive difference and I will put an estimate together of both methods before I choose which to use. I think both Telebeam and Ecotruss will do Supply-Only of galvanised joist lengths, and I imagine that there are also some local steel supplier who could be even more competitive on price. . Has anyone considered the above? I'd appreciate to hear your opinion.

"our 100mm 7n concrete paintgrade are manufactured to 10.5n strength". ^Could get a job as a script writer for a politician I know?

Yes I've thought about that method but personally I worry that large format tiles are more susceptible to telegraphing cracks from movement at substrate level; I have it in my head that grout lines provide some accommodation of horizontal movement, or at least that if there is significant horizontal movement the grout line will crack before the tiles. Also wont you still have grout joints crossing the floor? Although only a couple.

@SimonD Happy to have found this thread! I'm planning finishes for an upcoming build. I really dislike grout/grout lines; visually and practically, so I'm considering ways to avoid having and essentially that means using alternatives to tiling. Do you (or any other reader) have plans to use alternatives to tiles for the floor finishes in the bathrooms?

@MJNewton Thanks for updated the thread, good to hear that the roof is performing as it should!

@MJNewton Interesting read this, can you tell me how it all ended up? Reading through the thread I thought anything other than choosing Option 1 (leaving as is) would be madness; and then the plot twist with the suspect installation! I imagine with the fullness of time the integrity of the roof has been well tested now.

I should have been clearer, I'm referring to pipework serving heating/sanitary installation on the ground floor (say heating F&R to radiators, domestic hot and colds to WHBs) These are typical ran in the ground floor build up and turned up to their relevant radiator/sanitary ware. Personally I have very rarely seen that ground floor serving pipework ran at high level (be that within 1st floor joisting void or under 1st joisting/above a false ceiling )and then turned down the walls, although I can imagine there are benefits to it; such as easy of future access if needed

Totally agreed with all the above. Unfortunately advancement of better practices in the building game is frequently hampered by an attitude of "it's always been done this way" Any experience in running pipework under or in the 1st floor level ceiling void? This is typical arrangement in commercial project but I cant recall seeing this in domestic residential builds.

Tbh I think its common and accepted practice to have heating flow & returns fixed to the sub floor (lagged of course), not saying it is the most energy efficient. If fact I'm not sure how it could be avoided where wet UFH pipework is also being installed in the build-up? Of course the hot primary's could be ran under/in first floor level and dropped down to ground where needed. That is actually an arrangement I'd like to explore as it also would allow potential leaks to be much easily identified and accessed for repair.

Apologies, I didn't mean better performance in W/m.k but in that poured insulation is a continuous layer. I'm a carpenter by trade so relatively skilled at cutting, fitting and installations but even for me cutting in floor insulation around pipe runs is nearly impossible, its a very poor arrangement and surely a lot that PIR U-value performance is lost here.

Yes correct, AFAIK it isn't a substitute for the structural concrete subfloor; perhaps it can be designed so but in any case I am just thinking of it as an alternative to PIR. I think in any arrangement the DPM will always be located above pipework to ensure continuity but under the poured insulation. If I read you post correct you are essentially using this method but reducing the thickness of poured insulation in favour of PIR to meet U-valve? Its the junction of insulation (of whatever type) around the pipework that is problematic so I think you are hitting the mark with your hybrid design and it gets you over the pipework! Do you buy in ready mixed pourable insulation or does the contractor just site mix a lean mix with vermiculite? On my last project I first fitted 70mm PIR squarely ( not scribed to the pipework) to the floor fixed pipework, if that make sense, and then infilled over the pipework runs with a lean mix/vermiculite flush to the top of that first 70mm PIR layer. That got over the pipework and allowed a 2nd layer of 70mm PIR to run continually uninterrupted.

Make sure that the manufacturer of the render system use confirms how they want it done NOT the contractor. Weber for example can be very particular that these sort of details are built to their specif detailing, they will be issuing the warrant on the system so you must meet their specification.

Personally I'd raise this with SE, they should be specifying this detail for you not strangers from the internet! But yes, I've fixed a joist ledger board to a wall before with M12 studs (threaded bar) embedded in resin, its commonly used. However the frequency of the fixings and particular type of fixing should still be specified or at least ran by the SE for verification.

Morning all, I have been aware of TLA (thermal lightweight aggregate) as a construction product but more so used in large commercial projects but it now seems to be offered as a poured insulation subfloor to domestic project. https://www.energystoreltd.com/professional, this company seem to been a product wholesaler not a actual contractor. Just wondering if anyone has any experience of using this in a domestic project. In my experience fitting PIR floor insulation is a nightmare of a job for a whole range of reasons. Its a time consuming job, cutting the insulation around pipework to ensure a continuous fit of insulation all over the floor is near impossible and furthermore which contractors do you get to do it. A poured insulation seems to have many benefits, waste free, storage free, better performance. Is it not yet commonly used in domestic project due to cost or just hasn't been rolled out yet? Keen to hear your opinion!