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loft conversion advise. mainly floor joists

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maximus999

from United Kingdom

Joined: 29 Nov 2008
Posts: 58
Location: Durham,
United Kingdom

PostPosted: Mon Dec 01, 2008 11:03 pm Reply with quote

Hi all, this is my first post on this site and have a little knowledge with the terms and words what the builders use lol, I am wanting to convert my loft and trying to get some guidance on my floor joists i need to put in. My ceiling is being held up by 5x1 joists which are no good to lay a floor on, these run from gable wall to centre of the house were there is an 8x3 joist which runs from the front to back walls of the house which is a span of 28 feet which has a supporting wall in between which has foundations and in which the 8x3 joist rests on. . Is there a way i could reinforce these 5x1 joists up to support a floor? each are 11 feet in length and are spaced 400mm apart, i believe this could be done but i am not sure if the 8x3 joist is strong enough or is it? on the gable wall they meet there is another 5x1 which runs along the wall that they are secured to and cant suss a way out how i could strenghten them so the only way i can think of putting floor joists down is to go from the wall at the front and rear of the house to the centre wall which has foundations, the span from wall to wall is 14 feet, would 9x2 be strong enough on 400 centres to give a good solid floor? My next mission is when i redo the main roof i want to take some roof supports out to open theloft up to make it a straight walk through but want to make sure the roof dosent cave in lol. as you can see from this picture would it be ok to reposition the supports to go vertically down as illustrated? [/img]
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Deluks

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PostPosted: Tue Dec 02, 2008 3:48 am Reply with quote

Can't be a***d with a full in depth reply, but to start you off, I'd say use 9x3 for a 14ft span.

No you can't remove those angled struts and replace them with upright studs.*
As the current ones are being run onto a load bearing wall, and probably against it's opposite member which is countering the forces from the other direction. To change it to an upright will almost certainly channel the loads on the big rafter/purlin combo into your 5x1 ceiling joists.





*Although you could do it if you had a big steel in place to take the roof loading. (...and you thought you were being clever by thinking up an economical way to convert the loft... icon_wink.gif )
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maximus999

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Joined: 29 Nov 2008
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Location: Durham,
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PostPosted: Tue Dec 02, 2008 8:32 am Reply with quote

Thanks for the reply delux. o i now know i have to work around these struts supporting the roof which is not a major problem as i can walk through tha gap but it would have been good to remove. so 9x3 from front and back wall to the brick wall in the middle is my way forward then! if i do this would it make a difference if i notch the 9x3's at an angle to fit under the eves i think you call it were the roof struts meet the 2 outside walls at either end of the house. I have been over to b n q and they only do 9x2 is it detromental that i have 9x3? and how would it benefit from the extra inch, as the strength is in the opposite way or am i wrong on this one? Thanks Ian
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Deluks

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PostPosted: Wed Dec 03, 2008 5:50 pm Reply with quote

Proceeding as you are, this isn't a proper loft conversion, and will never be classed as such if you ever decide to sell. This will be a fair amount of work for little or no financial gain, but you will make the space more usable for storage/train set purposes.

Not putting a staircase in by any chance?

If you still wish to carry on with this 'posh loft' then you'll get away with 9x2, although don't get them from BnQ, they will be cheaper from a builders/timber merchant.

pack out under the ends of the new beams with some 18mm ply or timber, this will ensure that the bottom won't contact with the ceiling under deflection. I wouldn't fix them to the existing, place them just to the side.

You'll get away with sloping the ends of the beams, as closely to the eaves as you can.
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maximus999

from United Kingdom

Joined: 29 Nov 2008
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Location: Durham,
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PostPosted: Wed Dec 03, 2008 10:57 pm Reply with quote

Thanks again deluks!! I know that when and if we sell the house it wont be classed as a room and more of storage space but as things stand at the minute financaly we wont be selling the house, we cant have kids so its just us 2 and it is big enough as it is (but need an new project), anyways if 9x3 would be better then i will use them and thank you for the advise on this one. I will be putting a stair case in as we want to use the loft as a main bedroom, we live in an old miners cottage which has only one floor which is the ground floor and it would benefit us to use the loft space. i am confident in building works but as this is new territory i am seeking as much advise as possible before i eventually start it, i was quoted a price of 15000 pounds from a builder as he said it would need steel gurders and so on and we don't have this sort of money to spare without either getting a loan or remorgtage so we decided that we don't really want to move and that we would just go ahead and do it lol. If i go ahead and continue without planning permission from the local authority could i be prosecuted in anyway or get told to stop what i was doing if for some reason the council got wind of it???? next door to me have put a dorma on the back of the house as i type this, without any permission and i think they are on dodgy ground as i believe you need permission if you change the look of your property externally and if it can over look another persons property!! if this is the case rather than getting light via a dorma could you put velux windows into the roof without seeking permission? with regards to planning permission would i the best if possible to comply with any regulations which are standing i.e use a fire door to the loft and have a fire escape out of the room, thanks again for any advise in advance
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Deluks

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PostPosted: Thu Dec 04, 2008 3:30 am Reply with quote

Well if you are turning it into a bedroom and sleeping in it then you should still comply with full regs.
BUT, as you are not building on the third floor, as would normally be the case with a loft conversion, then you'll probably find that there are less regs to comply with. You will still need a compliant structural floor but might get away without the steel if you can find an engineer to design you an easier to install solution.
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chappers

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PostPosted: Thu Dec 04, 2008 6:48 am Reply with quote

You will almost certainly be able to get away without steel by using timbers bolted together.

Knock up a quick sketch with dimensions showing the supporting walls below and indicate where the stair will come up and i will probably be able to knock up something for you that will comply with regs for the floor, could also give you some pointers to insulation too and then you are half way towards a compliant conversion, which will add value to your house.
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maximus999

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Location: Durham,
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PostPosted: Thu Dec 04, 2008 9:26 am Reply with quote

Thanks for the info guys, by the way do yous not sleep lol here is a rough sketch for any advise probablys not the best architect drawing in the world but hope you understand regards Ian
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chappers

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PostPosted: Thu Dec 04, 2008 4:19 pm Reply with quote

Just had a look at your sketch with dimensions and it appears deluks has already given you the answer, if with a little overkill.

If your supporting wall is dead centre then 195 x 50 is right on the limits for that span at c16 graded timber for c24 the permissable span would be 4.5 m these could run from your wallplate to the spine wall in the centre and it would be ok to chamfer the ends to fit into the eaves.
If this spine wall is off centre then use this table to work out timber sizes

http://www.carryduffdesigns.co.uk/technical/floor-joists.html

With regards to removeing your purlin supports if you upgraded the floor joists to 195 x 75 c16 then you could remove the diagonal purlin support and replace it with a full length 100x 50 purlin wall built up off of the floor.

I would run a 195x 150 (3 No. 195x50 bolted together at 600 centres with M10 bolts and dogtoothed connectors)parrallel to the stairs with a 195x 100 hangered off this running to a shoe in the gable wall, with 195x 50s off of this to piece the floor in back to the eaves.

This would give you a floor structure that would meet building regs and for the sake of filing a building regs app you could have this on record should you or anyone else decide to do a full conversion in the future.

With regards to insulation You would need to insulate with 100mm rockwool inbetween the joists, (supported on chicken wire, unless the ceiling below is rated to 1hr.)

As for the roof100mm of rockwool with tri-iso 10 over the top should be ok , dependant on whether your LABC allows it, they do here. Otherwise 90mm celotex between the rafters with 10mm under(you may have to batten out the rafters so you can keep a 25mm air gap over the insulation.

Remember you have drawn your staircase coming into the pitch of the roof check to make sure you have 1.9m clear headroom over the sataircase( you may need to put a double winder staircase in to acheive this.
Electrics will need to be signed off by a qualified sparky.
Throw in a couple of veluxes and few stud walls and a bit of plastering and Bobs your uncle a loft conversion done to regs.

As Deluks says you are building on the 1st floor so shouldn't have too many fire regs to contend with, if any.
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maximus999

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Joined: 29 Nov 2008
Posts: 58
Location: Durham,
United Kingdom

PostPosted: Sat Dec 06, 2008 7:54 pm Reply with quote

Thanks for the detailed log which mostly flew over my head. lol I hae come to the decision that i will leave the purlins as they are not a major problem! you said i should "I would run a 195x 150 (3 No. 195x50 bolted together at 600 centres with M10 bolts and dogtoothed connectors)parrallel to the stairs with a 195x 100 hangered off this running to a shoe in the gable wall" what do you mean by dogtoothed and parrallel to the stairs, is this for to strenghten around were the stairs would come up? and the shoe in the gable wall do you mean notch the bricks out to sit the ends of the joists parralel to the way the floor joists run to support the opening?. and one last thing the 1.9m hight is that the clearence from the step that is vertical to the opening in the ceiling for the stairs as if to have head clearence when going up and down the stairs. regards Ian
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chappers

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PostPosted: Sun Dec 07, 2008 10:47 pm Reply with quote

When you bolt several bits of timber together to make a thicker beam you use what are called dogtoothed connetors threaded onto the bolt between each bit of timber. they bite into each bit of wood taking the load instead of it being put onto the shaft of the bolt, they look like this

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=120301212746&cguid=dc36373711c0a0e2045640e6ffcf4bfc

The triple beam running alongside the staircase is not so large to strengthen the staircase opening but needs to be beefed up as it will take the load of the beam ahanging off of it and indirectly the staircase as the beam running at 90 degrees going to the gable wall will be taking the weight of the stairs. You can build this beam into the wall if you like but a shoe is a bit more convenient and fits into the mortar joint.
They look like this except you would need a 100 mm one rater than a 50 mm one

http://www.screwfix.com/prods/99505/Building/Builders-Metalwork/Joist-Hanger-50-x-225mm-Pack-of-4;jsessionid=3E4TEGV0PKXHUCSTHZOCFFY

use plain starap hangers when fixing joists to the other timber beams.

The 1.9 mm is from an imaginary line connecting the nosings of the treads, also called the pitch line and relates to anything over the staircase be it the ceiling as you come up or your roof at the top.

If you are going to use the loft as a bedroom i would definitely remove the diagonal purlin supports and as I said just build a 4x2 purlin wall(essentialy a stud wall supporting the purlin).




The purple beam would be the triple 195x150 the blue would be the 195x 100 and the blacks would be your 195x75 floor joists make sure you have 1.9-2m clearance under beam B and 1.9-2m over beam A

Bear in mind that you may have to have turns in your stairs (probably at the bottom and the top)so you come into the room facing towards the purple beam to get the headroom and even then this may not be possible to get the rquired headroom[/img]
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maximus999

from United Kingdom

Joined: 29 Nov 2008
Posts: 58
Location: Durham,
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PostPosted: Mon Dec 08, 2008 10:46 pm Reply with quote

Thanks for the info chappers, things are starting to come together in my head to start and tackle this project but i have a few things just to clarify off the back of what you have suggested. Firstly you said you would remove the purlin supports which are currently like this . do I replace so that they look like this if i do this would i do it like this . With the purlins on an angle how would you suggest i use the 4x2 is this drawing sufficent? or is there another way to knotch the end of the 4x2 to addequatly hold the purlin securely? . The only other thing that is puzzling me is could i take the supports out which run up to the 5x1 and supports it? which are these I dont know if i could get a suitable size piece of timber to run from gable to gable to support the 5x1 which wouldnt sag like me nans belly Thanks again for your help Regards Ian
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chappers

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PostPosted: Mon Dec 08, 2008 11:26 pm Reply with quote

no need to double up any of your new 8x3 floor joists sit a sole plate across them directly beneath your purlin and support your purlins with notched 4x2 as you have suggested or remove purlin and replace with 4x2 and esentially build a stud wall down to your new floor joists. before you complete your stud wall you can also take out that big timber that runs up under the purlin from eaves to ridge from what I can see it isn't doing much more than supporting the prlin at mid span.
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maximus999

from United Kingdom

Joined: 29 Nov 2008
Posts: 58
Location: Durham,
United Kingdom

PostPosted: Tue Dec 09, 2008 7:26 pm Reply with quote

Ok chappers thanks for the info again, so you are saying i can romve the diagonal struts which run up to the 5x1 as you can see in picture, it is supporting the 5x1 purlin at the top were the rafters from both sides of the roof meet but it is a flimsy piece of wood nailed to the big joists, are you sure i can remove these and the roof wont cave in? because if i could remove them and the struts at the bottom the whole loft would be opened up then which would be magic. i looked at the nailed piece of wood earler this afternon and was thinking to myself it cant be doing much supporting. Thanks again Ian.
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chappers

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PostPosted: Thu Dec 11, 2008 2:30 pm Reply with quote

It appears you could remove all of these.
If I can see correctly from your photos, the big timber running up with the roof rafters is notched under the purlin and runs upto the ridge , where it meets the other one on the other side and then runs down to either the wall plate or more likely the big 8x3 that runs front to back.
I would build your floor first and then your purlin wall whether up to the existing purlin or seperately directly above or below it and then take out the big timber and struts as there is still quite a bit of weight on the roof from the tiles etc. Although in reality the purlin on it's own should take the weight fine for the amount of time it will be unsupported.
If I get a moment i will draw up aquick sketch as an overview of everything.
Cheers
gareth
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