Loft Conversion Floor

17 Dec 2012
Reaction score
United Kingdom

First let me explain that I am new here so if I don't get the protocol 100% correct please let me know and I will learn from my mistakes.

I am a fairly competent DIY'r and and currently considering a loft conversion. Looking at the floor joist span tables it appears that, luckily, the current joists are sufficient in all areas apart from one room where the span is over the limit for the dimensions of the current joists.
My Question: If I construct a box lintel (or other type of lintel) under the new stud wall, is there a type of joist hanger that will suspend from the lintel and attached to the existing joist, thereby effectively shortening the span. Without removing any of the ceiling? i.e bolt through the existing joist rather than loop underneath it?
Sponsored Links
Hi thanks for the swift response, The dimensions of the existing joists are:

C24 38 x 195 x 450 spacing

Most of the spans are under the limit but some are slightly over hence requiring support or new joists.
Those look pretty big joists for a ceiling.

Instead of putting a new beam in to shorten the span, why not beef up the existing joists by screwing additional timber joists to the sides?

Alternatively, slip some additional parallel joists in between the existing joists (if your spacing is 450, an additional joist between each one in the critical area will mean each joist is only then carrying half the weight).
Sponsored Links
Thanks for your replies so far

Tony1851: Yes they are large for ceiling joists, Luckily, I think the guy who had the house built in the sixties envisaged the loft extension. It's a detached bungalow and I think he could see it would make a good Dormer.

Woody: how would you pass the straps under the joists, would I not have to remove some the the plasterboard ceiling under each joist? I was trying to avoid this if possible.

Brilliant! I will get hold of one and give it a try.

Thanks for your help
Not sure what span tables you have been looking at, and not sure whether Trada tables are applicable in Jersey, but a C24 38 x195 at 450 centres will span 3900 with imposed load of 1.5kN/m2 and dead load of up to 0.5kN/m2
Would suggest you follow the advice by Tony, scissor bolt a C24 50x195 to existing joists and this will increase your span to approx 4500 all in accordance with above imposed and dead load.
If it is a traditional cut roof and eaves, the ceiling joists will be sitting on the external wall plate and partition walls, so have no idea what woody is rambling on about, as there are no fixings for long leg speedy straps, unless of course woody sticks them to the roofing felt with super glue.
Regards oldun
Hi Theoldun

The UK span tables do apply in Jersey. It is always difficult to get all the necessary info without drawings etc and given that all your advice has been very helpful. I think both solutions would be workable. One thing i did not mention was that there is a supporting wall mid span along 75% of the length of the loft meaning that the existing joists would easily pass building regs. for the other 25% I could use your method which is probably favorite or, as I mentioned and woody picked up on, I could construct a box lintel as part of the new eve side walls. If I then uses woody's idea of speedy hangers attached to the box lintels I would not have to deploy any extra joists as it would be almost exactly 3.9 meters between joist hangers. However, after considering all your advice, I think I am going to construct the box lintels and hang new joists between them alongside the existing joist and bolting them to the existing joists for addition strength. Thanks again for all your advice.
That is a great sketch and exactly my scenario. Thanks you both for your help. Both of you have given very valuable advice. This is the first time I have used this site and am very impressed with the help received.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links