New member..loft query!! please help!!

[adamfernadam]

Hi there i have just joined this site. i have read through all of the threads about lofts but im sorry im still confused thier is so much advice about!!! i live in a 1900 end terrace house and am just about to start my loft project creating a space that is only for light storage i.e boxes of clothes, xmas decorations etc nothing heavy!!!
The current loft hatch is tiny and situated at the top of my stairs which upon entering you are right in the eaves and have to about bend in half to get in. I am going to create a new hatch more centrally which i have no problems in doing.
My queries lie within the task of insualtig and boarding ( sorry if youv heard it all before)!! My loft consits of a truss at each end and one in the middle so 3 in total and between these run ceiling joists of 4" x 2" measurements spaced at 16". Each one runs from the truss at the end to the central truss covering a length of just under 7 feet unsuported in the middle. These hold up the bedroom lathe and plaster ceiling. In between these joists is 4" insulation. My plan is to raise the level of the insulation to 10" (the current reccomended level in new homes) therefore needing to raise the joists 8". I would then like to board this with MDF or chipboard or something to store my things on.
What is the best way to increase the height of the joists with a) making sure it is strong enough and b) not affecting the lathe and plaster ceiling below?
Do i glue/screw 2 4x2 upright on each joist? do i glue/screw 4 3x2s flat on top of each joist thereby giving me the height and also a better area to screw boards to? Do they need to be just straight on top of the current joist or need to be attached to the trusses? i am worried about the extra weight of wood/flooring on top of the current joists bringing the lathe and plaster down!!

PLEASE help me as i need to crack on, the wife is giving me grief about starting it...and i feel stuck!!! Dont want any accidents!! Thanks in advance!!

 

[biffvernon]

Sounds like a lot of work. Why not insulate the roof? Thermafleece could be attached to the underside of the roof, keeping your Christmas decorations cosy.

 

[adamfernadam]

the roof above is sheeted with the blue plastic with the white squares in it like a damp/vapour/draft barrier i assume?

i still want to board the loft out though and surely i cant just screw boards onto the existing old joists..the weight would bring the ceiling down no?

 

[arl]

we also have a terrace house (1890) and our loft sounds quite similar. we just put boards straight onto the beams. so far it hasnt collapsed but im no structural engineer

 

[middi]

If your ceiling joists are 4x2 supported well at each end, only seven feet long and there is no woodrot, they should hold up an elephant.

As Biff said , use thermafleece for that extra insulation value and just board over the existing joists.

 

[adamfernadam]

ok thanks for the advice...so not worth raising the joists at all? some are slightly uneven and i would like a level floor. with these ones woud it be best to screw something such as 2x2 on top of the existing joists?

 

[biffvernon]

Middi's right but don't try to get an elephant through the hatch.

 

[adamfernadam]

okay ha no elephants...just boxes and rubbish like that...has to support me crawling about though and im 16stone!!! so extra height,support or nothing?

 

[middi]

Repeat again.

If your joists are 4x2, only seven feet span and in good condition there is no need to add anything, honest.

If you are creating a new opening use another 4x2 as the trimmer, and if you want to level the ceiling floor, just use spacers or fillets where necessary.

Another word of advise, just use short or long screws as required, try to avoid any hammering of nails etc.. in the joists, the lath & plaster may crack or shake loose.

 

[adamfernadam]

okay thanks middi good advice!

I have had another look in the loft and a few of the joists are smaller or slightly rounded shapes..is this a problem? sorry if it sounds daft i just wanna be sure before i start..then end up bringing the ceiling down. im fine with making the new opening thats not a problem! They run from the wall at one end i think to a truss in the middle. then seperate ones run from the truss another 2 meters to the wall at the other end. dont shoot me down..i just wanna be 100% ok thanks for your help

 

[middi]

Well, obviously you do not have regularised 4x2 but a more "scantly" type of ceiling joists, this is why they are uneven .

Without actually seen them no one can really comment on what you are trying to do, or if they would be strong enough.

If you are unsure about their strenght or stability, just build another ceiling out of pressure treated 4x2 besides the existing joists( not on top ), screw them against the old joists and make sure they are supported at the ends.

This will strengthen the old ceiling and give you a level floor, most of all, it will hold up the " elephant" .

 

[arl]

we havnt got an elephant in ours but we have got 50 years worth of other peoples c**p . on top of this it has supported a water tank, me and my partner, a family of starlings and recently quite a large roofer and his assiatnt.
The floor was a bit tricky to lay but the worst was fitting a new loft hatch in a hole so skew it was almost a diamond shape

 

[Caitlyn]

Hi

My house is of similar age and construction in the roof space. We don't really use it for much at the moment so we haven't needed to consider it but when I was doing other structural work I found this really useful table for working out whether a floor span can take normal usage ie a person/storage/walking around/water tank etc.
Our surveryor didn't recommend using our roof space for anything more than books and light objects and spacing them around on the joists until we got the joists replaced though.

 

[middi]

There you go.

Now you can get totally confused at your own leisure

 

[Caitlyn]

Yeah sorry you're right it is a little confusing

4in = 101mm
2in = 50.5mm

so you measure the distance between the joists, for instance that is 400mm in my house.

So with 2x4 joists and a 400mm gap between you could run a 1.98m (6.4ft) floor span without any additional support from underneath or more joists. That would give you a floor that is safe to walk on and safe to put storage on.

Since you have a truss in the middle, you measure wall to truss on either side.

As you say not all the joists are exactly the same size so you need to find the smallest joists and work the calculation from those to be on the safe side. Also you need to remember that joists that have been cut out for electrics etc are weaker than a standard joist.

C

 

[biffvernon]

Yeah sorry you're right it is a little confusing

so you measure the distance between the joists, for instance that is 40mm in my house.

Yep -you're confused

 

[Caitlyn]

lol no just missing a zero (clearly that should have been 400mm), damned keyboard. Must be all the plaster dust!

 

[adamfernadam]

Thanks to you both for that great (slightly confusing) advice!!

The joists are 4x2 (slightly uneven in some places but generally that size).

And the span between wall and centre truss is 2.1m. so it seems its right on the borderline of being strong enough? Would it be safer in your opinion to just screw some say 3x2 along the top of each beam raising it slightly giving a level surface to board, and also to strenghten it slightly becasue of the weight of any boarding im going to use?

 

[adamfernadam]

Okay ladies and gentlemen..a new problem!

The joists the far side of the centre truss are 4x2 srewed to the centre truss at one end and fixed into the stone wall at the other.

The joists near side of the centre truss are DIFFERENT though...there is one 4x2 but the rest are small 3x1.5 inch joists attached again to the centre truss and into the wall at the other end. Im am very sure these will not be strong enough for one and also need to be level in order to board over..which they arent because of the varying thicknesses! :?

Any ideas? :?

 

[middi]

Couldn't you build a nice shed to park the "elephant" , it will stop you scratching your head about the loft.