Which joist hanger type and exactly where does it go?

[Notch7]

These are the nails for joist hangers:

https://www.screwfix.com/p/easyfix-square-twist-nails-sheradised-3-75-x-30mm-1kg-pack/12788

If you need to use the joists as rafter ties you will need to fix some against the common rafters

If you have a gable end, you may need to use some straps across 2 joists and fix to the masonry.

 

[antonyc]

Do I assume that you haven't submitted the plans yet, and the SE wil only do the plans and cals based on the 5.5m steel he wants to use. Maybe you need to ask him to justify his reluctance, and see if he'll do both calcs/plans etc, and then suggest he allows BC to make the final decision. If you point out the problems his insistance is causing, he may (I do say may) relent, and be a bit more amenable.

Hi, I haven't submitted any plans yet, but I've done all the architectural work myself using a tape measure and AutoCAD. I've also drawn up the plans myself too.

The first SE didn't come to the property, but looked at my plans, quoted £600 and said steel only. I asked him to consider timber, explained that I have a preference for timber, explained that steel would cost me more than twice as much to implement, explained that it messed my staircase design up and needed party wall agreement, and he still refused without a reason. He just reiterated; "I recommend steel".

I'm now in contact with another SE who has looked at my plans and said that my solution seems perfectly possible. He is coming to view today at 4pm in order to give a quote.

Bearing in mind that all I want to do is replace the ceiling/floor joists and remove the bracing between the two perlins, I don't see why this is so expensive in structural fees.

The floor joists in first floor covering the same spans are 7x2 and they are perfectly fine. So, how can 7x2, notched, chamferred, hung on hangers and nailed to rafters possibly not be strong enough? The current ceiling joists/rafter ties will remain in place AND I want to put collar ties on the rafters and a knee wall! Surely, this design would add considerable strength rather than weaken it!

 

[antonyc]

These are the nails for joist hangers:

https://www.screwfix.com/p/easyfix-square-twist-nails-sheradised-3-75-x-30mm-1kg-pack/12788

If you need to use the joists as rafter ties you will need to fix some against the common rafters

If you have a gable end, you may need to use some straps across 2 joists and fix to the masonry.

Thanks for the info!

The existing ceiling joists/rafter ties will remain in place as well as new 7x2 ceiling joists - maybe even also attached to the rafters!

I already have a bag of those sheradised nails from another roofing job I did. (My custom made shed roof)

 

[Notch7]

The first SE didn't come to the property, but looked at my plans, quoted £600 and said steel only. I asked him to consider timber, explained that I have a preference for timber, explained that steel would cost me more than twice as much to implement, explained that it messed my staircase design up and needed party wall agreement, and he still refused without a reason. He just reiterated; "I recommend steel".

SE's can be a funny breed -they can be quite offhand. Maybe its because they have to be resistant to builders trying to tweaks their designs.

Dont forget everything they provide calcs for is underwritten by their Professional Indemnity insurance so over engineering gives them a larger safety net.

Ive found a helpful engineer for our orangeries calcs. I do the design and specify the sections and he does the calcs based on that, if it doesnt work then he comes back to me. Otherwise the orangery design ends up looking wrong if the engineer specifies.

 

[Doggit]

Ah, I think I've spotted the issue. It's the bracing between the two purlins that needs the support. I suspec he would out the steel below the purlins, then then provide the dwarf wall support from that up to the purlin. Then you take the joists right across to the other steel. SE's charge so much, because their reputation is on the line, and they have to have adequate proffessional indemnity insurance to cover any problems.

Now you can leave the existing joists in place if you put the new wooden joists in between, but I suspect the joists would be in the way of the steel beams, so although the purlins would be supported by the beams, there'd still need to be a degree of lateral restrain somewhere. Now it could be, and the new SE will specify 8" joists, and they would support the purlins.

 

[antonyc]

Ah, I think I've spotted the issue. It's the bracing between the two purlins that needs the support. I suspec he would out the steel below the purlins, then then provide the dwarf wall support from that up to the purlin. Then you take the joists right across to the other steel. SE's charge so much, because their reputation is on the line, and they have to have adequate proffessional indemnity insurance to cover any problems.

Now you can leave the existing joists in place if you put the new wooden joists in between, but I suspect the joists would be in the way of the steel beams, so although the purlins would be supported by the beams, there'd still need to be a degree of lateral restrain somewhere. Now it could be, and the new SE will specify 8" joists, and they would support the purlins.

Correct! That is the main problem.

The new SE came to my property (what a nice guy), and he was very positive about timber-based construction. He said that my design appeared to be fine although he said not to notch and chamfer the joists because under excessive loads or stress, or in the event of movement, the bottom and top of the joist can split apart. Instead of that, he said to place them on hangers only and place a block behind the edge on the joist on the wall plate. He also said that I should raise the new floor above the old ceiling joists by x amount, not flush with them because we don't want to add any additional loads on those joists at all.

He confirmed that I'd need one UB to extend the load bearing wall to the gable to support a few joists. He made several suggestions/options regarding supporting the perlins and we agreed on a supporting stud wall which would transfer the perlin deflection down to the new joists. He thinks the new joists will probably be 7x2 but with possibly smaller centres.

Total cost for calculations; One UB to extend the load bearing wall, all floor joists and the new stud wall: £400 including VAT.

Does that sound reasonable?

 

[Doggit]

You didn't mention where the UB is being placed, but other than that, yes it looks good. But I'd still go with 8x2s.

 

[antonyc]

You didn't mention where the UB is being placed, but other than that, yes it looks good. But I'd still go with 8x2s.

Yeah, I haven't show you guys the full plans because I don't know if you have AutoCAD. The UB isn't going to be in the roof. There is a central load bearing wall in my house which supports the joists throughout the house, however, this wall doesn't go from gable to gable, and it would be a bit useful if it did. So where it stops, we're going to put a UB from there to the gable. Here's a pic: (Left is ground floor, right is first floor)

The rest of the house is done in 7x2s, so, I don't know. 7x2, 8x2, I guess I'll decide later on down the line when we decide we're going ahead.

 

[Doggit]

Then I think everythings been covered, and we'll see you back at the next stage of the job. Best of luck anthony

 

[cdbe]

Hi, I'm doing something like this at the moment, not a loft conversion but a stronger loft floor for storage using 7x2 joists. I abandoned the original plan of joist hangers off the wall plate to sit the new joists a few inches lower into the room below (to gain extra loft headroom) because the existing joists sat directly on the inner spine wall and I would have had to start cutting out or slotting the bricks to sit the new ones in. I ended up sitting them on top. The sistering with the existing 3" joists went out of the window as they had 40mm of deflection in the centre so ceiling would have been interesting as would doing the noggins. I cut out the old joists and put the new ones in their place with the eaves end chamfered, I'm happy with this - even though it looks like your SE wouldn't be . I swapped them one at a time and replicated the fixing to the wall plate and rafters and joists on the other side of the house. The other other thing is that if you're sitting the joists on the outer walls above any windows you'll need to check the lintels.

 

[antonyc]

Then I think everythings been covered, and we'll see you back at the next stage of the job. Best of luck anthony

Thanks so much for your help everyone! It has helped me to design my own loft conversion!

We're not going to go ahead with it just yet as I have some other jobs to finish first, but it's certainly the next major job.

I'm estimating that we will start within the next 3 months.

 

[antonyc]

Hi, I'm doing something like this at the moment, not a loft conversion but a stronger loft floor for storage using 7x2 joists. I abandoned the original plan of joist hangers off the wall plate to sit the new joists a few inches lower into the room below (to gain extra loft headroom) because the existing joists sat directly on the inner spine wall and I would have had to start cutting out or slotting the bricks to sit the new ones in. I ended up sitting them on top. The sistering with the existing 3" joists went out of the window as they had 40mm of deflection in the centre so ceiling would have been interesting as would doing the noggins. I cut out the old joists and put the new ones in their place with the eaves end chamfered, I'm happy with this - even though it looks like your SE wouldn't be . I swapped them one at a time and replicated the fixing to the wall plate and rafters and joists on the other side of the house. The other other thing is that if you're sitting the joists on the outer walls above any windows you'll need to check the lintels.

View attachment 134823 View attachment 134824 View attachment 134825 View attachment 134826

Hey, thanks for the pics!

 

[John D v2.0]

A bit late but it's an interesting thread.

Regarding the existing joists, when our SE came out one time I asked about how the existing roof was actually staying up, as there were just nails bashed through all the joints and not much triangulation otherwise, he just said they don't need to worry about how the existing stays up, otherwise they'd have to rebuild the whole lot.
I suppose existing construction has stood the test of time, anything that didn't isn't around any more! But he's not got to guarantee that.

 

[Bullet-Proof_Biscuit]

It's been 3 months...

 

[Ian H]

I saw some funny ones the other day: