Loft Conversion - New Joists unable to sit on wall plate.

[DynamiteMatt]

Hi,

Currently under way on a loft conversion looking for some advice on possible ways to attach the new joists without sitting on the wall plate, it would not be possibel for me to sit them on the wallplate without dropping the ceilings.

The existing joists are sat on a load bearing wall around the centre of the loft and either end (external wall ends) are just nailed to rafters with the rafters running onto the wall plate.
Now its specified I double these up with 75x200 c24 which is fine and in the architects initial visit he spoke about just fixing the new joists to the existing and splitting the span on the centreish load bearing wall, so new joists will be internal end sat on load bearing wall and external end bolted/fixed to existing rafter/joist. No steels.

Anyone out there had any expearience with this?

Building control made the architect add on ply collars either side of rafters at the top which im currently fixing, will this stenghen the rafters enough to take the extra load? Im yet to have been contacted by building control but should be any day now just dont want any nasty surprises the architect was confident and said i was free fire board the ceiling (which is now done)

I seem to have rambled on abit for a 1st post hope you can make sense of this.

Thanks
Matt

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[tony1851]

Hi,

sat on load bearing wall and external end bolted/fixed to existing rafter/joist. No steels.

Are you saying that the outer ends of the 75 x 200s are just fixed to the sides of the ceiling joists? And then additionally supported by plywood gussets attached to the rafters?
I'm not saying that wouldn't work, but I've never come across that way of supporting floor joists before. It would put a considerable load on the ends of the rafters. What supports the additional load over window openings?
Be careful about going too far. The Building Inspector will probably check with the Council's own engineer, and he in turn may then require stuctural calcs. The thickness of plywood, and nail type/spacing will be critical in proving it would be a sound job.

 

[DynamiteMatt]

Thanks for the reply Tony,
Just to point out first the floor joists have not been fitted yet. The architect we have used uses a private building control company that have viewed the plans, revisions have been made and then submited (plywood collars/gussets added)

Are you saying that the outer ends of the 75 x 200s are just fixed to the sides of the ceiling joists?

Yes the plans just show the new 75x200's fixed to the existing joists (pic of existing below)
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Now I just cant imagine that building control would just let them get fixed to the existing, I wondered about suggesting fixing a noggin between the rafters and using a hanger to hang the new joist inplace?

The ply collar/gussets which where added to the plans were specified at 18mm ply screwed every 75mm, Pic below of one partly fitted with 47x100 fitted between rafters to.
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[freddiemercurystwin]

Ooh I don't like private inspectors, especially when they work in conjunction with the same people all the time. I like your good old trusty Local Authority.

Anyway I'd get an SE to look at it if the Private Inspector doesn't bat an eye. How is your architect qualified in this way?

 

[DynamiteMatt]

Ooh I don't like private inspectors, especially when they work in conjunction with the same people all the time. I like your good old trusty Local Authority.

Anyway I'd get an SE to look at it if the Private Inspector doesn't bat an eye. How is your architect qualified in this way?

I work in a builders merchant and every builder I work with warned me off the local authority route and numerous recomended going with this architect.
An SE has looked at the plans but has said he doesn't need to do anything, I was kinda looking for some details on the fixings/joins from the SE but I dont want to go looking for another bill.

 

[freddiemercurystwin]

Well that's why you're on here though isn't it, cos your architect/SE have done a poor job.

Any builder who's afraid of an LA BCO has something to hide IMO. They get an easier ride from the private inspectors as they tend to be more lenient and do so because they like to keep in with the builders to make sure they get the next job not the LA. Its all too common. But the client is none the wiser and is the one who loses out.

 

[DynamiteMatt]

Im on here looking for some options, the architect and building control will make suggestions as to how I end up fixing the joists im sure, i'd just like to see what options are out there.

When we first took on this project I contacted the local authority first who were not very helpful other than suggesting using an architect and referring me to the goverment planning/building reg websites and told me to come back with drawings and an application.
It was suggested from multiple people that I use an architect and private building control I would get much more guidance through the project.

 

[freddiemercurystwin]

Its a common misconception that Building control are obliged to help with how to achieve things they're not. Anyway I've worked with countless LA BCO's from about 5 different councils and can count on one hand the times they've been anything but helpful.

I've never seen a loft done in this way so cannot help with your original query but then I always use an SE.

 

[tony1851]

Hi,

it would not be possibel for me to sit them on the wallplate without dropping the ceilings.

Is it in fact not possible to sit the joists on the wall plate without lowering the ceiling? Why?
In cases where we have not used steel, we have sometimes sat the joist-ends on the wallplate (tops need to be chamfered to clear the tiles etc). Its a bit of a pain but can be done, and would be better than trying in effect to suspend them from the ends of the rsfters.
Take heed of the other advice offered here.

 

[DynamiteMatt]

Is it in fact not possible to sit the joists on the wall plate without lowering the ceiling? Why?



The ceiling height is higher than the wall height by about 200mm.

 

[tony1851]

The ceiling height is higher than the wall height by about 200mm.

Ah, I understand now - you have a collar-braced roof. These roofs are difficult to fit floors in.
As the new floor joists will be supported off the rafters at some distance up the slope from the wall plate, this will put even more stress on the rafters, which are probably only something like 3x2.
The more I read on this, the more I think you could be heading into trouble.
I know ths is a DIY site but IMO you really need to speak to an independent SE, at least to get another view on this.

 

[DynamiteMatt]

Thank you for your input Tony I shall take it on board.

Matt

 

[field82]

Matt

Did you get this resolved? I have a very similar problem.

Thanks

 

[Dant17]

If you are fixing the new joist to existing rafters it might be a good idea to strengthen the racer by bolting a larger rafter up the side first

 

[Adam182]

Any updates from either of you? I'm also currently faced with a pretty much carbon copy situation... Thanks