New joists in loft

[Furious Pilgrim]

Afternoon all,

I'm looking to add new joists to my loft before I put some flooring down. The existing ones are only 2x3, and I would feel more confident if bigger ones were installed. I've looked through loads of threads on here which have helped, but now I'm stuck.

I was going to run the new joists resting on the brick at the front/rear, and have them overlap on the supporting wall in the middle. Problem is, the front/rear wall doesn't come up to the height of the joists. In all the rooms upstairs, the outer wall slopes at the top. Hopefully shown in the pictures.

It looks like the joists run the full length and attach to the rafters?
What are my options?

 

[^woody^]

One option would be to post the pictures.

 

[Furious Pilgrim]

Bear with me, net just went down, trying to sort it on my phone ️

 

[Furious Pilgrim]

 

[tony1851]

You have a collar-braced roof, which is difficult to add joists to.
All you could probably do is screw the new joists to the sides of the rafters, level with the existing ceiling joists, overlap them on the central wall, and hope for the best.

 

[Furious Pilgrim]

Super. At least I know what I'm dealing with now.

 

[Furious Pilgrim]

Any more for any more?

 

[John D v2.0]

Not from me, but we have exactly the same system in our roof and only one person on our side of the road has done a loft conversion. On the other side with similar houses with a standard roof, about half have. So must be difficult.

 

[John D v2.0]

Also when Tony says screw, that would put a shear load on the screws so make sure they're rated to handle that. Standard screws are very poor in shear.

 

[tony1851]

Coach screws would be best.

 

[Furious Pilgrim]

If the strength of the screws is all I have to worry about, happy days

My main concern was the new joists putting strain on the roof structure where it was never intended to have it. I have a tendency to over analyse and over engineer things.

I had just thought about running joists in a criss cross over the top of the old ones, but didn't think it was the 'right' way of doing it. Although a few companies are advertising doing it this way.

Main thing is I wanted to add strength, not do anything to compromise the roof.

 

[John D v2.0]

Whichever way you do it you'll be adding the self weight of the new joists plus whatever you plan to put on there to the rafters, this will apply to the ends of the rafters causing some extra shear and to the wall plate.
I'll be interested in what you do in the end since our roof is exactly the same!

 

[Furious Pilgrim]

Never liked being the guinea pig

 

[John D v2.0]

haha sorry Mr Pilgrim! Well, I'd do it sooner if we had the funds

But in all seriousness, if you do design it yourself, don't go storing boxes of books and magazines up there, as the weight can build up! Christmas decorations on the other hand, that would be fine! Also, if you post your updates on the Your projects section as you plan it, I'm sure people with more knowledge than me will point out before you go wrong.

 

[Furious Pilgrim]

That's just it, I have some heavier things to store up there, hence wanting to beef things up a bit.

Considering getting a structural engineer in to have a look. I'm the type of guy that once I know what I'm doing, I'm good to go. Just don't want to make any mistakes. Haha