Loft floor advice?

[Ian H]

Hello,

We are thinking of making a loft room but I can't think how the floor would be supported.

The house is a 3 bed semi, hipped end with a solid internal wall that goes 2/3rds of the way across the centre. It's been empty a while and the upstairs ceilings were in poor condition so we have pulled them down.

I would have bolted a length of 8x2 to the wall and hung 8x2 joist from that BUT the wall plate is below the current ceilings, it's 10mm back from the inner face of the bricks and if I bolted an 8x2 below it my new ceiling height in the bedrooms would only be 216cm which I think is too low.

I'm not sure if I could get 125mm hangers to fit to the wall plate and sit my 8x2's in them? Or if I could fit the 8x2's on top of the wall plate and loose 125mm off the loft height.

If possible I'd rather not disturb the existing 75x50 joists but would like to maintain the current height in the loft.

Does anyone have any advise that could help? Thanks very much.

Here's is a picture of how it is now.

 

[Doggit]

Not sure if you can do this with 75x50 ceiling joists, but you'd fix a 100hx75w beam into the junction between the roof joists, and the ceiling joists, and then nail your joist hangers into that. I assume you have a wall running along the centre of the house that you'd then run your joists on to. What's the width of each of the rooms upstairs, and how long would the joists be.

 

[freddiemercurystwin]

Are you talking about a proper loft convertion or is this just some playroom deathtrap accessed by a ladder for the kids?

 

[Ian H]

Freddymercurystwin, A proper loft conversion if I can fix a decent floor and keep good height in the bedrooms as well as the loft. Otherwise it's a non starter.

Doggit, do you mean build up ontop of the existing wall plate? The one fitted is 110mm wide and 85mm high.

There is a wall in the middle, the back bedroom span is 3.2mtrs and the front is 3.4mtrs

 

[Doggit]

No 1990, It was a trick the local Building control officer told me about. I had 3" ceiling joists in my loft, and the BCO told me I could push the 4x3 beam into the angled space where the ceiling joists, and the roof joists met, as the loading would then be fairly close to the wall plate. With the 3" of ceiling joist, and the 4" of 4x3 beam, he then wanted 6"x3" floor joists, and finally agreed on 6x2 - which was a mistake with a 4.4M span, but a manageable one. You set the new floor joist in the centre of the old ceiling joists, and leave about an inch gap below them so the new floor, and the old ceiling don't touch.

 

[chappers]

Get the whole thing designed properly by a structural engineer, put a steel in above the ceiling ties and span off those to the centre spine wall and then from there to the rear wall plate, avoiding point loads over any windows. Get it designed properly BC will want to see calcs anyway.

 

[securitynewbie]

Sorry to jump in on this thread, but I'm in exactly the same position as 1990 (see my other thread).

You mentioned to get a proper structural engineer for a steel girder, but just as an approximate, what would this cost and how much roughly can a couple of 12ft steel girders cost?

Also how would one get a large steel girder into the loft?

 

[Ian H]

We have had a guy design a loft for us, he has done a drawing which is having a few tweeks before he submits it to the council for approval.

 

[Doggit]

I couldn't give you prices, but the steel can be done in 2 halves, and then bolted together. In you're case security, you'd set it under, or slightly forward of the lowest rafter support.

 

[Mikefromlondon]

Hello,

We are thinking of making a loft room but I can't think how the floor would be supported.

The house is a 3 bed semi, hipped end with a solid internal wall that goes 2/3rds of the way across the centre. It's been empty a while and the upstairs ceilings were in poor condition so we have pulled them down.

I would have bolted a length of 8x2 to the wall and hung 8x2 joist from that BUT the wall plate is below the current ceilings, it's 10mm back from the inner face of the bricks and if I bolted an 8x2 below it my new ceiling height in the bedrooms would only be 216cm which I think is too low.

I'm not sure if I could get 125mm hangers to fit to the wall plate and sit my 8x2's in them? Or if I could fit the 8x2's on top of the wall plate and loose 125mm off the loft height.

If possible I'd rather not disturb the existing 75x50 joists but would like to maintain the current height in the loft.

Does anyone have any advise that could help? Thanks very much.

Here's is a picture of how it is now.

View attachment 95245

I think many people have not understood your question properly, your ceilings are out already, so it is the best time to add or replace the 75x50 josist you have, indeed, and you want to use 8"x2" joists, which i believe is an overkill, since your main objective is height in both the loft and the room below, not compromising the strength..

So your biggest span is 3.4meters or approx 11 foot, and you could easily use 6.5x2.5 in joists, and place them a little more closely. This could rescue you instead of using 8x2 spaced more far apart. So immediately you have gained 2" in your room below.

I live in 1930s build houses where floor joists are 6.5x2.5" at every 14" interval never had any issues with any floors bouncing. This is in my living room where we often had large gatherings and party dancing with a cellar below. and my span is at least 12 feet, and even longer into bay window, but it has 4x4 beam over the bay.

question....are you going to remove the existing 75x50 joists? if so beware the roof joists (rafters) may be nailed into the floor joists, and I wouldn't want to disturb this.

 

[Ian H]

I'm finally cracking on with this and am just thinking about the floor while I'm at work.

I need to put a steel across the back bedroom and bathroom which is a 203x102 UB. I am going to bolt a timber into the web and hang 8x2 joists off that. I'm wondering should I use a 7x2 in the web or should I machine an 8x2 to make a perfect fit? Also should I be bolting a timer to each side of the UB or just to the side that the joists are coming off?

 

[Doggit]

I live in 1930s build houses where floor joists are 6.5x2.5" at every 14" interval never had any issues with any floors bouncing

The caveat here, is that 1930's timber was slower growing, so a lot stronger. A 1930 6.5" joist would be the same as an 2015 C24 8" joists. I did my loft conversion 10 years ago, and the BCO wanted 7x3s, but finally agreed on 6x2 C24 at 14" centres, and admittedly they are 4.2 spans, but boy do they bounce. Should have listened to him and gone with the 7x3s that he originally wanted.

I'd bolt a 7x2 into the web (only one side), and then hang the 8x2 off it with joist hangers. You can tuck the top of the joist hangers into the top of the timber, and then wedge a piece of wood in to the gap for extra security.

 

[Ian H]

Thanks for that

Our plans say 200x60, I've not checked with the guy but I'm guessing that's suppost to say 200x50.

 

[Doggit]

More than likely. Query it, and check to see if it's available locally..

 

[chappers]

I'd bolt a 7x2 into the web (only one side), and then hang the 8x2 off it with joist hangers. You can tuck the top of the joist hangers into the top of the timber, and then wedge a piece of wood in to the gap for extra security.

Or nail a timber to the top of the steel and then fold the hangers over the top and nail