joist thickness for loft conversion

[jaysta]

Hi there,

I have a mid-terrace house that was built in 1880s. I've pottering about in it doing work here and there. I've left the worst thing til last now come to sort out the main bedroom. The plaster isn't looking too clever on the walls and ceiling is sagging badly.

The ceiling is a lath and plaster ceiling and it seems that the joists that the ceiling is holding on to is are bowed... causing the ceiling to sag.

I'm looking to rip down my main bedroom ceiling. I also want to replace the joists with much more substantial ones but since I've purchased this house I've always had this idea that I want to extend upstairs into the loft with proper stairs going up as well.

Currently the joists up in the loft are 3" x 1". I've had a couple of suggestions from people I have spoken to about doing this have said that 6" x 2" should be fine. I'm not convinced... my joists on the upstairs floor are 7" x 3" so how can 6" x 2" be any good?

I'm planning on using upstairs for something like a chill-out room and having my PC and that kind of thing up there. So the problem there is that with even this kind of use I'm being told that this classed as habitual so I need to comply with Building Regulations.

So far (and please feel free to correct me if I'm wrong and/or point out anything else I haven't found out yet or considered), I've found that the stairs must go to the landing and have a fire door. The headroom clearance all the way up the stairs must be 2m. I know the new ceiling must be the fire grade (pink coloured?) type.

My question is this: What thickness joists should I consider using? The distance between front wall and middle wall (the existing 3" x 1" joists rest on this middle wall; the distance is 3.97m and from middle wall to back wall is 4.07m. Also, what joists would I need just for using the loft space as storage? The reason I'm asking this is because of my budget and may not be able to afford doing the loft conversion completely unless I can get the joists in first and consider stairs and rest of conversion later.

Sorry for the long post and thanks for your time; I appreciate it.

Jay

 

[Chukka63]

First you need to establish if the middle wall is load bearing.
If it is then its ok. You will need a minimum of an 8"x2"/9"x2"

If its not youre going to need some steel.So contacting a SE and getting some calcs is the next step.When/if you decide to go ahead you will to get Building Regs or work under a Building Notice.

You may be tight on head room if you have to use steel and remember your ceiling heights will be reduced too with all the insulation needed these days.

 

[freddiemercurystwin]

So far (and please feel free to correct me if I'm wrong and/or point out anything else I haven't found out yet or considered), I've found that the stairs must go to the landing and have a fire door. The headroom clearance all the way up the stairs must be 2m. y

You do need a fire door at the top or bottom of your new stairs, the headroom required for a loft conversion is 1.9m above the centre of a stair http://www.planningportal.gov.uk/Pp...gportal.gov.uk/uploads/br/BR_PDF_ADK_1998.pdf diagram 3 page 7.

 

[Chukka63]

You do need a fire door at the top or bottom of your new stairs

ive just completed a loft conversion and there was no fire door top or bottom.is this regulation then????

 

[freddiemercurystwin]

You do need a fire door at the top or bottom of your new stairs

ive just completed a loft conversion and there was no fire door top or bottom.is this regulation then????

Definately

 

[Chukka63]

thats a bit odd then as full building regs per submitted at the planning application stage and the BCO never mentioned it at all etc.

 

[freddiemercurystwin]

Rather odd indeed, was it a bungalow?

 

[jaysta]

Cheers Chukka and Freddy for your replies. I've got a few more questions.

First you need to establish if the middle wall is load bearing.

Well, when I've been lifting the floorboards up on the upstairs floor to make improvements to electrics, alarm and central heating I've seen that the 7" x 3"s are going into this wall from the front wall and the back wall. This makes me certain this middle wall is a load bearing wall.

You will need a minimum of an 8"x2"/9"x2"

What grade are we talking here? I know the 6" x 2"s were C16?

...So contacting a SE and getting some calcs...

I take it this is a Structural Engineer? How much do these people cost?

You may be tight on head room if you have to use steel and remember your ceiling heights will be reduced too with all the insulation needed these days.

I'm really hoping that this isn't the case because the highest point in roof at one end is 7' 1" and t' other end is 7' 4". If I was to go ahead with the 6" joists I would lose 3" in the loft, which I would have tolerated but now I'm wondering if perhaps I need to go completely below the upstairs ceiling height to make it to regs as much as possible and use the 8"/9" joists.

Actually, this was my original intention tbh but my builder friend said it would be ok with the 6" joists and talked me round into not destroying all the ceilings because the bathroom and back bedroom ceiling are not bad. [sigh] This is getting a bit frustrating now.

Thanks again though guys for your input

 

[jaysta]

You do need a fire door at the top or bottom of your new stairs

ive just completed a loft conversion and there was no fire door top or bottom.is this regulation then????

Definately

I've recently been in touch with a BCO at the council that I work in and he said to me that you can get away with not having a fire door if you have hard wired smoke detectors in place as this would give you your early warning. I'm not sure if he said that they have to be in every room though. He also said that it depends on the BCO you talk to.

I'm going to quiz him a bit more about the joists as well I think and see what he says. Whatever I find out I will post back on here.

 

[jaysta]

Today, I asked the BCO at the council I work in and he says for the spans I have mentioned 8" x 2" joists at C16 grade minimum (which he says what are provided as standard by timber merchants) are needed as this would cover a span upto 4.39m.

So thanks again guys; you guys were pretty spot on with that.

 

[freddiemercurystwin]

He also said that it depends on the BCO you talk to.

Yes this is the problem, it will depend who is inspecting your project.

 

[squarenut9]

Today, I asked the BCO at the council I work in and he says for the spans I have mentioned 8" x 2" joists at C16 grade minimum (which he says what are provided as standard by timber merchants) are needed as this would cover a span upto 4.39m.

So thanks again guys; you guys were pretty spot on with that.

Sorry to slide in on the side guys. Im in the throws of doing a loft conversion myself on a 1948's bungalow from scratch. I have been involved in several when I used to have my own electrical business, so I drained my builder freinds for the latest rules and reg for free. But it seems regs have changed a hell of a lot since the 1990's.

There is a rule stating that I wont need PP unless the floor area is over so much square meterage. I phoned up my local authority and they wouldnt tell me unless I gave them the location. I didnt stay on the phone after that.

I have the same measurements/ span, about 4mt, and I am wondering if 8 x 2" would bounce. I was considering 9 x 2". Is that OTT do you think?? Also I believe the joists have to be independant of the original 3 x 2" ceiling jiosts AND closer together, about 400mm centres apart. Is that correst.
How do you tie the joists together to stop them twisting, its not as simple as putting the galv strapping or noggins as the 3x2" ceiling joists will get in the way. Sorry for all the questions, hopefully somebody out there will know the answers.

 

[jaysta]

There is a rule stating that I wont need PP unless the floor area is over so much square meterage. I phoned up my local authority and they wouldnt tell me unless I gave them the location. I didnt stay on the phone after that.

There is this document but... it doesn't mention bungalows unless they come under detached?

I have the same measurements/ span, about 4mt, and I am wondering if 8 x 2" would bounce.

Try this link it's got the information there; however I don't think it's up to date. If anyone else can find an up to date reliable table then please post. Again, I'm not sure if this is different for bungalows.

 

[hotrod]

There is a rule stating that I wont need PP unless the floor area is over so much square meterage.

You generally will not need PP for a loft conversion unless your house is listed or in a conservation area as long as you are only installing velux type windows. IIRC If you want to make changes that come forward more than 100mm from the existing roof pitch PP will be required. BRegs will be required regardless.

I have the same measurements/ span, about 4mt, and I am wondering if 8 x 2" would bounce. I was considering 9 x 2". Is that OTT do you think??

8" x 2" C16 @ 400 centres are within tolerance for a 4m span so will be ok. Herringbow struts or noggins for restraint.

hth

 

[Tipper]

The old edition of Building Regs Part A, 1992 issue, give tables of timber sizes for spans, etc.

You can still find this on the web whereas the newer version keeps it secret, can't see why!