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Hello all, Our current 1st floor consists of 40x210mm joists (unstamped but assumed to be C16) spaced at nominally 600mm centres. Based on the increased dead load from removing the old paramount partitions, replacing with 38x89mm CLS studwork with some acoustic insulation, replacing the chipboard subfloor with this floating acoustic subfloor and adding an overlay underfloor heating system, a structural engineer has recommended reinforcing the floor by adding additional joists in between the existing joists by building into the external walls to bring the nominal spacing down to 300mm centres. What would be the best way of installing these new joists? The existing joists are either built into the external walls or rest on masonry joist hangers on the party wall. I was initially considering raking out the mortar joints, filling with fresh mortar with a mortar gun and installing masonry joist hangers to match the existing joist hangers but a civil engineer work colleague recommended against this. He was uneasy about there not being adequate compression of the mortar if retrofit this way. I really want to avoid building these new joists into the wall as I doubt I would be able to cut the holes at the right height and size without making a mess of it and I expect it would take a really long time. I wouldn't want to do this to the party wall anyway as it would compromise the acoustic performance of the party wall. The other solution I'm considering (pictured below) is installing ledger boards between the existing joists and installing joist hangers off those, but I'm not sure if that would be a good idea since the external walls consist of hollow concrete blockwork. From my online searches I can only seem to find American examples of fixing ledger boards to cinder blocks to build outdoor decking. Does anyone have any views on this?

So I’ve just started hanging my first floor joists with joist hangers. What a pain these are! 20 nails in each hanger and 12 of them are hard to get to! This is going to take me forever to do at this rate. Does anyone have any tips to speeding this up? Thanks!

Hi, Head is a little done in with personal stuff at the moment, but I have to try and get my head around the best way to fit posi joists into different materials I have. I'm very keen to not have deflection/bounce, so the joists will be at 400 centres. 1. Into ICF. So I will be having a timber plate bolted into the ICF face/concrete core for the joists to fix to. Are there 2 options here - 1st is on hangers and the 2nd is on the top chord of the joist? 2. Into RSJ webs. Does the joist just simply sit into the RSJ web? I may have an option of changing the RSG for a posi joist, would that be better or worse? 3. Into load bearing 100mm block walls. Should I fix into the block work as it's built, or bolt a timber to the side of the blocks and fix the same as I would with the ICF walls? Are all joist hangers made the same or do some makes fix better than others? I've also seen mention on a post about face fix and top fix hangers. Any advice would be really appreciated Cheers Vijay

Hi All My first post - so a bit of a rookie! I am designing a flat roof back and side extension to my Victorian Terrace and I want to expose the wooden joists of the flat roof into the exposed steel beam (like in attached pictures) I am trying to work out how these are fixed into the beam which is a UC 254x254 - obvi the traditional approach would be pack with timber + hangers but as it will all be exposed Id like a more aesthetic solution. As far as I can tell, I need a 'nice' looking hanger to fit inside of the beam that can be painted with intumescent paint along with the beam and am looking for recommendations for these. Or, do steel companies design this into the beam as it looks like in some of the pictures? I did email one to ask but the answer was no. Any recommendations for these as well! Thank you in advance.

I need joist hangers for two types of job: one to support a flat roof, the other to support a floor. Looking at the range joist hangers makes me feel like I'm in a toy shop. I like them all, but haven't got a Scooby about which to choose. Here's an image search for what's available. Presumably I would not choose a hanger with a top flange for the POSIs which are under the first floor (because it would make the flooring less even). Bearing in mind the horror stories related elsewhere on BH, which should I avoid (cheap?). Or is it a matter of - they are all OK, it's just how you use them that counts?

I get that masonry wall floor joist hangers are favoured over traditional in-wall fixing of joists in the pursuit of airtight homes but can these hangers cope with 100 years of cyclical loading? Here is my beef. Driving a metal nail into a brittle masonry block to attach a hanger feels like an abuse of such dissimilar materials with long-term failure designed into the fixing. Next add 100 years of 80kg cyclical loading as humans walk around inside the home, stir in some thermal expansion and contraction loads on the hanger attachments and surely after a decade or two the hanger nails will start wobbling in the blocks? Then finally for a laugh apply that process to light thermal blocks. Are my concerns unfounded? The no nonsense commercial builder of a plot nearby has fitted his metal web floor joists direct into the inner blockwork and these blocks are heavy structural blocks I think.