Best method to strengthen a loft floor ?

kwano

Standard Member
Hi all,

It's my first post after alot of reading and absorbing !

I'm kinda in mid flow of converting my loft and so far a Velux window and loft ladder has been fitted. The room will be non habitable and will be basically used as TV/office room and therefore I am not looking to apply for planning or building regs.

My house is an average semi with 3 sloping sides to the roof with substantial purlins to each side of the roof holding up the rafters (like a U shape from above). Between the front and rear bedrooms there does appear to be a solid supporting wall which is not in the centre from a loft perspective as the front bedroom is larger.

The current joists are approx 3 x 2 and would be looking to install new joists of 4 x 2 to retain some height. I would like to install a good strong floor but I am not intending to have anything too heavy in the loft. I am not looking to put in steels or anything on this grand scale.

From what I've seen and read can anyone advise whether it is acceptable to hang your new joists from a trimmer joist which hangs from each side of the purlins. I am not sure whether the purlins are strong enough to take the weight and if it is safe ?

I've attached a couple of photos from other sites where it looks as though this method has been adopted but a I can't confirm for sure.

Anyone's feedback and advice is greatly appreciated.
 

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MarkP80

Active Member
Hi there,

First of all, I'm no expert, so this is all opinion....
I've had a loft conversion done in the past, and haven't seen anything done by hanging from purlins. But it doesn't seem the right way to go to me. I would expect that would be more likely to give a flexible floor.
Really you want to try and set the new joists on the outside walls. You should also pack them up a little, as the ceiling (and old joists) is meant to be independant from your new fllor - so any floor deflection does not transmit to the celing below.
4x2 seems a little shy too, don't you think? It does depend on span, and I'm sure with a bit of research you could find some appropriate tables. But, if you're going to all the effort of putting the new joists in, you don't want to be disappointed with the results do you? I've got an extension in my house where what look like 4x2 joists have been used, but these are supported on stools down to concrete at very regular intervals, probably every 4' or so.
If you're in doubt, I'd seek further advice from a builder, or even your council building inspector may give you some advice. If you say you're only making a store room, for example, they do have the tables for joist spans, and I've always found them very helpful.
Consider installing a linked, mains powered smoke detector too.
I understand that you don't want to make it a bedroom, but you're still putting a lot of work in, so you may think a bit of extra work will give you peace of mind.

Cheers,
MarkP
 

velvitjester

Active Member
as long as your not gona be stamping on the floor,just sister the joists (ie brace another joist beside it using glue and bolt through)
 

Peter Parker

Distinguished Member
I'd do as velvitjester has suggested and use 6 x 2 beams sistered against the existing beams. Make sure they run to the same supports as the existing beams (probably outside walls and central wall). 6 x 2s will add quite a bit more strength and reduce 'spring'.

If you can space them a little higher as Mark has said that would prevent any direct interference with the existing ceiling. For added fire protection you could lay strips of plasterboard between the existing joists first and also use that as the spacer (seal edges with plaster). You can also use hanging wire baskets between the joists and fill with rockwool. This will further add not only insulation but stop it from falling through should there be a fire below.

I thought purlins were there to support the roof joists and tiles (plus a layer of snow), and adding any more weight to them above a layer of plasterboard may be asking too much. I guess it depends on how much weight they are originally intended to take. I had a house surveyed some years ago and one of the things it suggested should be done was to increase the size of the purlins because new tiles had been fitted and they were a heavier tile than was originally layed.

Gary
 

kwano

Standard Member
Thanks for everyones feedback :thumbsup:

I could possibly increase the joist size to 6 x 2 but was thinking of saving as much height as possible.

I have the opinion that the purlins cannot support extra weight and i do not believe it is good practice.

I would probably look to use the sistering method and 'pack' it a little higher to avoid any 'disturbance' to the original ceiling as suggested guys. The only issue maybe is my original joists do not sit directly on top of the wall plate. They are fixed slightly part way up the rafters as the ceiling is raised and from the internal corners of the room they are curved. I'm probably not describing too well so I've attached a little diagram with the profile section which hopefully explains it better ? Can you still fix at this same point ?

Another issue. As the angle is quite narrow where the joist meets the rafters and with the roof tiles on top there isn't much room to do anything. How does one work and fix new joists in ?

I am seriously thinking of getting someone in with the experience and knowledge to get this section of work done and hopefully the next can be a little plain sailing :)

View attachment Roof Profile.doc
 

Peter Parker

Distinguished Member
Have you walked around the loft area and how do the joists feel? I'm guessing that with the joists being fixed as they are it is OK to support the ceiling weight, but not a great deal more (does there feel like there is a lot of give?). I'd agree with you on getting some proffessional advice to be on the safe side.
 

johnone

Standard Member
i enquired about doing the same thing as you after seeing those web sites and building regs and planning permission are needed, as well as proper stairwell, you wont get building reg approval without one:thumbsdow
 

n0chex

Distinguished Member
I think the planning permission is only needed if for instance you sell your house and want to class the loft as another room , if that was the case you need a some serious steelwork up there a stairs and most the doors in your house changing to firedoors.

In your case if its for personal use or storage no planning permission is needed please someone correct me here if i'm wrong.

I have started my loft like you and my ceiling joists up there was only 3x1 , i opted for 4x2 and now my floor is solid with no give whats so ever plus i have had false ceilings in the bedrooms so no chance of cracking the plaster from above as the new floor is suspended also .
 

MarkP80

Active Member
Hi,

You don't need planning permission, it's building regs approval. (You sometimes need planning permission for a dormer window if you're fitting one, but usually only if it's on the front elevation).

i opted for 4x2 and now my floor is solid with no give whats so ever
- it all depends on the span really. The longer the distance between the supports, the greater the deflection for a given joist size. 4x2 may work for you - when I had my loft converted, it had to be 8x2!! There will probably be a difference though in what will flex when you walk on it, and meeting the loading requirements for habitable rooms as defined in building regs.

Plenty of people convert lofts for "storage" use. Obviously it can't be classed as a room as such if you come to sell the house. Planning permission not required. If you want it to be classed as a "habitable" room, then building regs apply, otherwise it's a storage room. If you don't go for building regs, then strictly speaking you are breaking regulations (along with many many others throughout the land!), whether you wish to sell or not. Change of use is the issue, even if it's for your own use.

The room will be non habitable and will be basically used as TV/office room
- TV/office isn't non-habitable. That counts as change of use, so building regs would apply. Non-habitable means storage, you don't have to sleep in it for it to become a habitable room.

Building regs covers a multitude of things -
Floor joist loadings, as discussed
Fire protected access (self-closing fire doors on all doors to the stairwell)
Linked smoke alarms on all floors (you're increasing the number of floors in effect).
Staircase to specific gradient, tread size and headroom dimensions
Sound inhibition to floor below, and to neighbours via partition walls
Thermal insulation and ventilation for the roof.
Part P regs for the wiring

Mainly safety stuff, hence my recommendation that even if you don't go for building regs, you should consider the linked smoke alarms for your own safety.

Not trying to put you off, it's up to you if you go for regs or not, as that makes it a far, far bigger (and more expensive!) project. Get the floor right though, as it's structurally important, and peace of mind is worth a bit of money IMHO.

HTH,
MarkP
 

n0chex

Distinguished Member
Good Information and advise here MarkP80.
 

s2holdings

Active Member
Good Information and advise here MarkP80.

It is good advice from Mark, but i may add you do not need an adition staircase to get access if you are creating 1 room. A secure loft lader is permitted. If you are to create 2 additional rooms then you need a staircase plus you need to meet all the fire regs aproval such as means of escape 30 or 60 minute fireratings for ceiling etc..

Speak to the council and they will give you all the info you need.. Also you will need a structural engineer to sign off the floor design to say that the floor is sound and secure before you will get building reg sign off. If you do not get building regs then you run the risk of invalidating you house insurance and also you may come into problems when you sell you house.
 

wandgrudd

Active Member
It is good advice from Mark, but i may add you do not need an adition staircase to get access if you are creating 1 room. A secure loft lader is permitted. If you are to create 2 additional rooms then you need a staircase plus you need to meet all the fire regs aproval such as means of escape 30 or 60 minute fireratings for ceiling etc..

Speak to the council and they will give you all the info you need.. Also you will need a structural engineer to sign off the floor design to say that the floor is sound and secure before you will get building reg sign off. If you do not get building regs then you run the risk of invalidating you house insurance and also you may come into problems when you sell you house.


got any thing to back that up. as it differs from every thing building control and the council have told me up until this point.
 

theatre-aholic

Standard Member
well i need to tell my builder to strengthen the floor so after he does i will tell you how he did it, this will be after thursday
 

Dr E

Standard Member
Ive just strengthened my loft floor. I've not gone down the regulations route as it's not going to be used as a bedroom. It's mainly going to be used as a chill out tv room for the kids.

It has a drop down loft ladder with handrail and a roof velux.

The existing beams were just the bedroom ceiling joists which were about 75mm x 4omm. A weird size I know but the whole house is weird.

I just placed 4x2 alongside the existing beams and placed these about 3" into the inner walls and bolted these to the exsisting beams. These new beams are now supported by the inner walls, internal bedroom walls and the old beams.

I then put noggins between these new beams. And chipboard ontop of these.

It's now very solid indeed with no flexing at all.

Hope this helps.

Mick
 

MarkP80

Active Member
but i may add you do not need an adition staircase to get access if you are creating 1 room. A secure loft lader is permitted.
- OK, there is provision in the regs to permit a ladder, but not one which can be put away, and only if you can't fit a stair in (Part K for stair details and part B for fire escape requirements for anyone interested.) -
"A fixed ladder should have fixed handrails on both sides and should only be installed for access in a loft conversion, and then only when there is not enough space without alteration to the existing space to accommodate a stair"

Also you will need a structural engineer to sign off the floor design to say that the floor is sound and secure before you will get building reg sign off.
- that's not my experience. The building inspector will be happy to sign off without any calcs if the joists used for the span meet the requirements as laid out in load tables thay have.

If you do not get building regs then you run the risk of invalidating you house insurance and also you may come into problems when you sell you house.
- When you come to sell, as long as it's described as a storage room, then there'll be no problems. As to insurance, not sure where the invalidation comes from. As always, don't mess with electrics if you're not competent, but even part K allows you to do a fair bit yourself. If you're not confident, get an electrician to do the electrics.

Ive just strengthened my loft floor. I've not gone down the regulations route as it's not going to be used as a bedroom. It's mainly going to be used as a chill out tv room for the kids.
- which is exactly what a lot of people do Mick. You don't have to go for building regs, and if you don't want it classed as a bedroom when you sell, then the approach is fine, IMHO. There's plenty of ways to strengthen a floor to an acceptable level too. As I say, building regs require the floor to be strengthened to meet specific loadings so that it will be good for any domestic loading. You are unlikely to need that level in just a tv room. If you put a big bath in there, it might be different!

As always, this forum is a good place to discuss these things, for everyone to pool ideas and experiences and opinions - that's why we all come here! :thumbsup:

MarkP
 

Peter Parker

Distinguished Member
Good info again Mark, thanks.

- When you come to sell, as long as it's described as a storage room, then there'll be no problems.

MarkP

That was exactly my experience.

I 'converted' my loft into a room with projector, screen and av gear with 4 seats to watch movies. It had an escape Velux (just in case) and linked smoke alarms. It was an ideal space because it had perfect light control.

When I came to sell last year, I made sure it was described as 'comfortable storage' or similar and it wasn't put in the house info as a habitable space as such. I explained that to the parties who were interested and eventually became the new owners, and there weren't ant problems with the survey etc.

In fact the new owners wanted the projector and screen left in place and that was part of the sale. That worked out fine for me since I currently don't have room for a projector (but that will change) so overall it was a good for both parties.

When I had converted the loft back in 2000, I told my insurance and they were perfectly happy with it, and didn't require any additional premium.

Gary
 

kwano

Standard Member
Wow I've just logged on and lots of great feedback and some interesting comments ! :thumbsup:

Gary, the current floor appears to be fairly solid when walking around normally. Not much give if any can be felt. I guess the supporting wall appears to take most of the load.

Ljw2k, I've seen your thread 'Loft home cinema room', some great pics and shots of your job. Great work. Those joists look pretty beefy and look more substantial than 4 x 2 (first thoughts, look more like 6 x 2 !).

Theatre-aholic, would be interested to learn what your builder suggests and recommends. And if its going to be costly !

Dr E. from the sounds of it your joists run left to right (or right to left) rather than front to back (or back to front) and hence you can fix to the internal walls. I guess the party wall rule would then apply ? Have you got any pics which you can post ?

Mark P80, thanks for the concise and clear information.

I think I will get a couple of quotes from builders and get some feel for prices / recommendations .... the job may get done a lot quicker that way ! (moans from the wife) :nono:
 

MarkP80

Active Member
I think I will get a couple of quotes from builders and get some feel for prices / recommendations

- Keep us posted with how you get on!

That worked out fine for me since I currently don't have room for a projector

- Just noticed the addition of "old" in your signature Gary. You'll have to get that sorted!

MarkP
 

Beaker

Active Member
Mark gave a load of good info, I have had a loft conversion done and it is habitable so I had to have 30 min fire rated door to the room, and escape window to the front. I have a proper staircase going upto it. The ceiling joists were left in place but 6"x2" joists were put in to support the floor. 90mm of Kingspan insulation between the roof rafters plus 25mm of Kingspan at 90 degrees to the joists covered in 12.5mm plasterboard. Same for the side walls into the eaves. That was all to meet building regs. Builder did the floor joists and stairs, I did the rest.

Cheers
Beaker
 

Peter Parker

Distinguished Member
- Just noticed the addition of "old" in your signature Gary. You'll have to get that sorted!

MarkP

I know!

It's frustrating not being able to make a start on the theater room in the 'new' place, but I have plenty of other things to keep me busy before hand unfortunately.

I'll certainly post my progress here once I make a start though. :)

Gary
 

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