Advice and thoughts for a loft conversion (Lots of pics attached)

[antonyc]

Hi Everyone!

I'd posted about this last year, and now it's the time to start planning it properly. What are your ideas on how you'd tackle this?

This is what I want to do: I want a livable space and I want to remove the purlins. I want to fit a few windows, preferably dormers. The stair case will go where the first pic is.

The area of the loft is 8m x 5m. There is a chimney present, however, it isn't used and I've already had the top of the stack removed in preparation for this project. The roof has been sorted out accordingly.

I'd say my DIY skills are pretty good, but I'll be carrying this out with a professional builder also. I intend to pay a structural engineer for calcs. The project won't be liable for planning permission.

Of the three main ways, there are RSJs, huge wooden beams or joist hangers, I think I'm more inclined to do the latter because RSJs are mega expensive and are a nightmare to get in! Apparently, even the huge beams need some sort of metal support too.

I'm just looking for some tips and people's opinions.

Here goes:

North facing, right side.

North facing, left side.

South facing, centre.

West facing, gable end (shared as I'm end of terrace)

West facing, showing gable end and south facing rafters.

South facing, right side.

East facing gable end showing south facing rafters.

South facing rafters.

East facing shared gable end showing chimney (the chimney is redundant and open at the end, within the loft.

Same.

Patched up roof after chimney stack removal.

Showing rafters and ceiling joists with some sort of filling brick over the wall plate between rafters and joists.

Thanks everyone!

 

[bobsuerita]

your engineer will tell you what needs doing and for steels there no biggie each beam can be cut into 3 sections and bolted together in loft

 

[Doggit]

You're either going to put in a steel below the purlins, and then support the rafters, or replace the purlins with a steel, which would be easier, because as you need 135mm of insulation, the steel replacing the purlin will be close to the insulation needed. Either way, you're going to need a party wall agreement with your neghbours.

But looking at the pictures do you have the height necessary; and do you have a load bearing wall running below the ridge line. If you do, then you'd wedge a 4x3 beam at the junction of the rafters and the ceiling joists (some authorities may want a flitch beam in there) and then put your joist hangers on it, and put 8x2 C24s in between the eisting joists, across to the cente wall.

You need an airflow up and over the room, so you batten out the rafters, put cellotex in between them, fill any gaps with expanding foam, and then add insulated plasterboard on top at right angles to get the necessary regs. Obviously, you'll build the dwarf wall up to the perlins, or up from the steels, and you'll need to insulate the end walls as well, keeping in mind that if you're bringing the stairs up against on the the side walls, then you'll need to take into account the insulation on the wall above it.

Personally, I'd avoid dormers, and see if you can do it under permitted development with velux windows.

Obviously this is a generalisation of what you'll need to do, taking into account what the SE suggests and you're BCO specifies.

 

[antonyc]

You're either going to put in a steel below the purlins, and then support the rafters, or replace the purlins with a steel, which would be easier, because as you need 135mm of insulation, the steel replacing the purlin will be close to the insulation needed. Either way, you're going to need a party wall agreement with your neghbours.

But looking at the pictures do you have the height necessary; and do you have a load bearing wall running below the ridge line. If you do, then you'd wedge a 4x3 beam at the junction of the rafters and the ceiling joists (some authorities may want a flitch beam in there) and then put your joist hangers on it, and put 8x2 C24s in between the eisting joists, across to the cente wall.

You need an airflow up and over the room, so you batten out the rafters, put cellotex in between them, fill any gaps with expanding foam, and then add insulated plasterboard on top at right angles to get the necessary regs. Obviously, you'll build the dwarf wall up to the perlins, or up from the steels, and you'll need to insulate the end walls as well, keeping in mind that if you're bringing the stairs up against on the the side walls, then you'll need to take into account the insulation on the wall above it.

Personally, I'd avoid dormers, and see if you can do it under permitted development with velux windows.

Obviously this is a generalisation of what you'll need to do, taking into account what the SE suggests and you're BCO specifies.

Thanks! I want to avoid steel because it's really expensive, and I can't do it myself either as it needs expensive equipment, crane, etc and several people. I'd prefer to use timber as I can actually work with it.

I'm not sure about the height, I'd have to chamfer the new joists I think. I do have a load bearing wall, it's the centre wall.I don't understand what you mean by "the junction of the rafters". I understand the rest.

Can I build the dwalf walls from off timber beams instead of steel?

 

[Doggit]

Look at the last picture, and that shows where you need to place the 4x3 beam to put the joist hangers on. Once you've got the joists in place, you can then put your floor in, run a floor plate along where you want the dwarf wall to go, and then put the uprights in. If you put a steel in, it'd be placed beneath where the purlins are running in the same direction as them, and then you'd support the rafters off of that, and that's allow you to remove the purlns, but you need an SE to work everything out for you, and to get it past building control

Some people suggest that you place the joists alongside the existing ones, and sister them together, but I opt to put them in between the existing joist, and seperate the new floor from the ceiling below. I converted my loft, and left the wooden purlins in place, and I then raised the cross members (as in picture 4) to ceiling height. How high are your purlins, and could you place the dwarf wall under them, or would you want it further back.

Sorry, but not sure you mean by chamfer the new joists.

 

[chappers]

your engineer will tell you what needs doing and for steels there no biggie each beam can be cut into 3 sections and bolted together in loft

exactly. Get your SE to design both if you like, but he will charge you for that. you might find that using timber alone may make the beams prohibitively large or that they are of a size that impinges on your available space/headroom.
It can, as you know be done in timber, but that isn't always the most efficient way of doing it, both practically or financially.
Out of interest how much height do you have from the spine wall to the bottom of the ridge board.

 

[antonyc]

Look at the last picture, and that shows where you need to place the 4x3 beam to put the joist hangers on. Once you've got the joists in place, you can then put your floor in, run a floor plate along where you want the dwarf wall to go, and then put the uprights in. If you put a steel in, it'd be placed beneath where the purlins are running in the same direction as them, and then you'd support the rafters off of that, and that's allow you to remove the purlns, but you need an SE to work everything out for you, and to get it past building control

Some people suggest that you place the joists alongside the existing ones, and sister them together, but I opt to put them in between the existing joist, and seperate the new floor from the ceiling below. I converted my loft, and left the wooden purlins in place, and I then raised the cross members (as in picture 4) to ceiling height. How high are your purlins, and could you place the dwarf wall under them, or would you want it further back.

Sorry, but not sure you mean by chamfer the new joists.

I still don't know what you mean about the 4x3 beam, I can't think of where the beam could go. I'll have a think. I thought the joist hangers would go off the wall plate. I understand about the dwarf wall. I want to remove the purlins because they are too high up. I can't remember the exact measurement though.

Chamfer the new joists because at one point, I wanted to rest the new joists on the wall plate, but there isn't enough space to fit them in.

 

[antonyc]

exactly. Get your SE to design both if you like, but he will charge you for that. you might find that using timber alone may make the beams prohibitively large or that they are of a size that impinges on your available space/headroom.
It can, as you know be done in timber, but that isn't always the most efficient way of doing it, both practically or financially.
Out of interest how much height do you have from the spine wall to the bottom of the ridge board.

Ok, headroom isn't an issue. There's plenty of headroom. I'll measure it next time I go up there, but it's got to be 3m or so. I think the consensus is to get an SE involved. The problem I have is that I want to do this cheaply. New RSJs cost a fortune. I can find second hand 5m ones cheaply but again, it's getting them up there. I've seen online that you can get stuff like two 9x2s and bolt them together to make a huge trimmer which is seated in the wall.

Hmmm...

I'll have to get an SE involved.

 

[chappers]

yep all perfectly possible, just give your SE the heads up about how you want to go and before you engage him ask if he is happy to design in timber for you. Does sound like you have plenty of head room, but if your thinking of creating a dormer to the rear, bear in mind the ridge support alternative in timber might be quite large, just be aware that, that head height gets eaten up very quickly once you take into account new floor timbers, flooring then ridge beams, insulation etc.
With regards to the purlins, again you will need to check with your SE if the purlin wall can be moved further down the rafters. In all honesty unless they are so high that they impinge on an area that you can stand in I would leave them where they are and build the purlin wall up to them and then build some eaves storage around them, bear in mind they will be another 6-8 inches closer to the finished floor too.
Get your SE on board early doors, some of the structural decisions you make will effect the design.

 

[Doggit]

Sorry Anthony, I'm not sure if I can explain it any better. You are assuming that you have to champer the ends of the joists to get them to sit on the wall plate, but you've then got no way to secure them. But if you were to take a piece of 4x3 wood (half the length of the room, and push it along the joist towards the outside wall as far as it will go towards the wall plate, it'll come up against the rafters, and you can then fix it in place down there. And if you've set it so that the 4" ( check with the BCO) side is upright, you've then got a wooden beam that you can fix the joist hangers to. And your new floor joist go from the joist hangers to the wall in the centre of the house.

Are you in a terraced house, or is there an outside wall. You can put up scaffolding, break a hole in the roof, and take the beams up through that, but as one piece RSJ has to be longer than the room, you need to knock a complete hole in the wall at one end, push the beam through it, and then manoeuvre it back into the other wall. If you can find a local fabrication company to drill the joist and provide a clamping plate, then you can cut it in half yourself with an angle grinder. Anything's possible with a bit of tenacity, and a lot of courage.

 

[bobsuerita]

the chamfer your talking about wont work as you only have 75mm rafters @40 degree(roughly) you wont get the full joist height bearing
you will need rsj's to take new floor and roof load
speak to an engineer he will most probly suggest placing to beams below purlins ( if dormer 3rd for ridge) its that simple with timber to support flor and roof your looking at big beams
also try to look at room size where your purlins are as moving room out further from these will need rafters beefing up as your increasing span

 

[Ian H]

I've bought a few RSJ's and thought they were quite cheap.

I tried to calculate my own beams on our loft conversion. If I were to do it again I'd get an SE in straight away. In the end paid £250 (haven't actually paid yet) for a SE to do the calculations for our loft conversion and roof extension. Money very well spent, he changed the design slightly by adding 2 small steels which will make the job much easier and I'd say stronger, it's something I wouldn't have ever even thought about.

 

[Red_Shift]

The "loft conversion manual" on Amazon is how I planned mine and it answers most of your questions. I didn't find rsj to be very expensive and they can potentially be bolted together in situ. A bigger thought might be whether you have services e.g. plumbing or electrics currently sat lying in the loft that need to be moved to fit new floor joists. You might need a fire proof escape corridor to the downstairs which could be an additional cost.