Floor Joists

[Fraser Lamont]

Hello 

i have an issue with a renovation project. I have a house to renovate, 1.5 storey. The upstairs was, shall we say - unofficial. Building control don't care, the house is nearly 50 years old and I believe B/C only have 20 years of enforcement on a particular property. Since the house came like this, it has Grandfather rights, even though I have a Building Warrant to 'Cathedral Ceiling' half the house. The entire house is being renovated. My current issue is the First Floor Joists - these are 2"x 6". The house is double block, there is a load bearing wall running the length of the house (12.5m from internal gable to gable) and the internal width of the house is approximately 7.4m. There is an open span of approximately 3.65m on either side of the 100mm wide load bearing timber wall. The block walls, as typically of Highland Houses of the time, must have had a concrete pour done at the top of the walls to create what is essentially a ring beam. The wall including cavity width is approximately 275mm, there is a 30mm thick top plate fixed to the inner block leaf (hardwood - looks like mahogany) and the ceiling ties are fixed to that. There is a board fixed to the ceiling ties  running down the length of the house and the rafters are fixed through this board into the top of ceiling ties/first floor joists (looks like it does the exact same job as a ridge board - only keeps everything in line). I have sistered half the ties with 47 x 150 (on one side of the load bearer), bolted at 600mm centres using M12 Threaded Rod and Square Washers with Nyloc Nuts. My Engineer seems happy with this, but what if I want to add deeper joists like 175 x 75? The reason I have sistered the joists right now - I will be collapsing the load bearer to fill in the underfloor void on the ground floor, adding around 80 ton of hard core, slab, rebuild load bearer then insulate and screed over underfloor heating. The span of the new timber I have kept at 4.8m to overlap the load bearer and the ceiling tie join above the load bearer and bolted it all the way to it's end. Main problem I have is deeper floor joists if fitted between existing ties - how can these be fitted to existing top plate? I can't fix hangers  because between existing ties there are only voids. Picture attached for clarity. Do I fix timber between all current ties with brackets and then fit new joists to them or is it just as well to continue with the sistering of 47 x 150 to the original 50 x 150 - and what is anyone's thoughts on the sistered joists? There is going to be 1 large bedroom in the upstairs space with an ensuite shower room (abs plastic shower tray, not stone), there will be a fitted wardrobe and another cupboard. Basically, there will still be less weight on the floor than there has been for most of the last 40 odd years, there was 3 or 4 rooms in the upstairs space until I stripped the house over the last few weeks. Thank You

 

Edited November 10, 2021 by Fraser Lamont
different image

[markc]

Loads of details but after reading this last night and again just now, I still cannot get the picture in my head of what you are doing or wanting to know.

a sketch or two? And or specific questions? I’m sure this is why no one has responded yet.

[Gone West]

10 hours ago, Fraser Lamont said:

Do I fix timber between all current ties with brackets and then fit new joists to them or is it just as well to continue with the sistering of 47 x 150 to the original 50 x 150 - and what is anyone's thoughts on the sistered joists?

Was there much deflection on the original joists before sistering them?

[Marvin]

1 hour ago, markc said:

Loads of details but after reading this last night and again just now, I still cannot get the picture in my head of what you are doing or wanting to know.

a sketch or two? And or specific questions? I’m sure this is why no one has responded yet.

+1  Is @Fraser Lamont saying he wants to take the middle wall running down the centre of the building away to sort the floor?

Edited November 11, 2021 by Marvin

[Fraser Lamont]

41 minutes ago, markc said:

Loads of details but after reading this last night and again just now, I still cannot get the picture in my head of what you are doing or wanting to know.

a sketch or two? And or specific questions? I’m sure this is why no one has responded yet.

Thanks for your response. I'm after advice on whether it's worth going with 47x150's bolted at 600mm centres to original 50x150's (not glued) plus nailed at 400 centres (alternating) or whether I should add deeper joists in between the original joists - any new joists would just have to sit on top of the walls and be nailed directly to top plates. Here's a wee sketch of the floor plans, top plan is Ground Floor. The ensuite door wall on the bottom plan is directly above the central load bearer.  The left hand side of the house I'm not concerned with, I'm building a structure at halfway and at the Gable end to carry a Glulam at the ridge which will carry new 10x2 rafters. 

[Fraser Lamont]

22 minutes ago, Gone West said:

Was there much deflection on the original joists before sistering them?

hardly any. Timber from the 70's seems a lot harder than the stuff we get now. Here's an image of the front half of the house, from front wall to load bearer. I bolted through the original joist connector pieces, the bolts are approx 200mm spacing over the load bearer, then 600mm for the remainder of the span. This is the image I sent to my engineer and he is satisfied with it.

[Fraser Lamont]

31 minutes ago, Marvin said:

+1  Is @Fraser Lamont saying he wants to take the middle wall running down the centre of the building away to sort the floor?

No, I'm doing that anyway (removing the central load bearer), to get the ground floor done. Problem I have is the load bearer sits on doubled up Ground floor Joists, the load bearer is approx 50mm offset from the dwarf wall. I have to remove the load bearer to get the floor joists out. I would have been able to sort all of this in situ if the load bearer was not offset - by cutting the floor joists and packing between the dwarf and the load bearer but I don't have that option. Once the ground floor void is filled and with a new slab at dwarf wall level, the load bearer will be put back up again

Edited November 11, 2021 by Fraser Lamont

[markc]

If this is only a temporary measure (taking the walkout) then as long as you don’t load the joists from above they don’t need anything as they are technically in tension with only self weight causing deflection.

[Fraser Lamont]

2 hours ago, markc said:

If this is only a temporary measure (taking the walkout) then as long as you don’t load the joists from above they don’t need anything as they are technically in tension with only self weight causing deflection.

it is a temporary measure, however I'll be reinstating the load bearer once the slab is down. The top of the slab will be level with the dwarf walls which gives me about 150-160mm, enough for 100mm PIR, underfloor heating and a screed - the floor will be approx the same level as it is now. I've bolted the new joists (150 x 47) at 600mm centres, I will be firing nails in at 400 centres to keep everything knitted together. The span is a few mm over 3600, I guess I'm hoping the paired joists will be ok at that distance. To be honest, the upstairs has been used for decades with no obvious problems. If I have to add new joists in between I'll have to go down the route of 75x175 or similar, any higher and the upstairs gable window would look daft. 

[markc]

46 minutes ago, Fraser Lamont said:

it is a temporary measure, however I'll be reinstating the load bearer once the slab is down. The top of the slab will be level with the dwarf walls which gives me about 150-160mm, enough for 100mm PIR, underfloor heating and a screed - the floor will be approx the same level as it is now. I've bolted the new joists (150 x 47) at 600mm centres, I will be firing nails in at 400 centres to keep everything knitted together. The span is a few mm over 3600, I guess I'm hoping the paired joists will be ok at that distance. To be honest, the upstairs has been used for decades with no obvious problems. If I have to add new joists in between I'll have to go down the route of 75x175 or similar, any higher and the upstairs gable window would look daft. 

Yes you will be fine