Strengthening a loft floor

[softyengin]

Hi, I have a new build 'SEMI-DETACHED' wimpey 'Tiree' house, 5 years old now, with W trussed rafters.

The wife is a teacher and is accumulating teaching materials like there is no tommorrow. also we now have a baby so our storage requirements have markedly increased!!

What i want to do is re-enforce the loft to handle storing lots of books, notes, folders, toys and everything else we can shove up there to create more space within the living areas of the house.

I've been told that the current loft can only handle a few things plus the weight of snow on it.

So i think i need to get something done to strengthen it, i should point out I have a LOT up there already and it seems fine but i just dont want to risk it anymore!

The specs are 7 metres (23 feet) front to back, 4.8 metres (16 feet) wide
The current trusses are 10cmx3.5cm or (4"x1.5") and are spaced at 600mm centers, with 9 trusses overall.


Either I do some work myself or get somebody in, but it seems relatively 'easy' to do?


My initial idea was that seeing as i just want to store 'stuff' up there, would be to run new thicker 8"x2" joints alongside the current ceiling joists.

In essence create a new floor resting on the front/rear timber frame but not touching the original ceiling joists.

I realise that I would probably need more than one piece to run from front to back! span tables etc... so i was thinking of using multiple coach

bolts (would that be best way to join them?) to securely join them together, and finally laying insulated flooring over them for the stuff to sit on.

is this easy enough? I've not actually crawled to the edge of the roof yet, but generally in a timber frame build, what should i expect to see?

Will there be an obvious thick beam at the edge that I can securely lay my new 8x2's on? anybody got a side on diagram of what it may look like?

(as you can tell im not familiar with what an actual timber frame looks like under its skin! but i want to learn)


If thats all OK, a current show stopper for me is there are what i think are called noggins? running perpendicular between the floor joists. I

think they are to stiffen the trusses so they dont fall over.

obviously these are gonna be in the way of my new bigger floor joists! can i remove them one at a time, put my new joist in and re-add them back in somehow?


so in summary i want to add new floor joists onto the existing timber frame with wood thats more than twice as thick as what I currently have, so should be more than strong enough!

Many thanks for any advice guys...

 

[Static]

Just fyi, standard trussed lofts are designed to take a storage load of about 0.25kN/m2 your new joists could take 0.21kN/m2 (before they start to sag the ceiling) so your actually putting in weaker members than the trusses..
Just bolting them to the trusses means just adds dead load to the trusses.. Might want to consider splitting the span up with a couple of steel beams and doing a semi conversion of the space, then you could put whatever you like up there on a floating floor.

 

[softyengin]

Hi Thanks for reply.

I wont be bolting to the original trusses, i intend to run these new ones seperate to them but alongside, ie no connection.

i will also be using thicker wood than the original trusses, can you tell me how the loads you mention are worked out.

how will my thicker trusses take a lower load? this stuff is all new to me, thanks guys

 

[Static]

Hi Thanks for reply.

I wont be bolting to the original trusses, i intend to run these new ones seperate to them but alongside, ie no connection.

i will also be using thicker wood than the original trusses, can you tell me how the loads you mention are worked out.

how will my thicker trusses take a lower load? this stuff is all new to me, thanks guys

What you intend to do is go from trusses to single span joists.. by nature trusses can be thinner as they have diagonal members framing the load up and creating intermidate supports within the frame.. the 7m spanning single member even being 2x as thick would be very very flexible and bouce like a trampoline..

Ignoring the truss chord, and just using the new joists for support, and lets say 0.5kN/m2 loading over the loft.. would need something like 50x250mm C16 joists at 400 centres.. could reduce the depth a little if you screw down some boarding..

End of the day thats only what 50kg per square meter storage.. so dont pile the books up too high.. also over 7m span its going to be very bouncy so noggin it up..

 

[softyengin]

Thanks for the advice static.

Ah right, I can understand that such lengths would be bouncy!

I will def be flooring the joists. I reckon i could just add these to one specific area of the loft to be used for storage and i can have light stuff stored on the regular trusses.

If i floor it do i still need the noggins or will the flooring board do the same job.

right im going to go up tonight and see if I have space for such deep wood on top of the timber frame/under roof bit

 

[JohnD]

if you floor it with WBP ply (18mm is usual for floors but 12 or 15mm should be OK for a light-use loft) in the largest pieces you can manoeuvre, screwed down tightly, it will add more rigidity than chipboard. Use noggins anyway under all joints and screw the ply to them.

 

[softyengin]

reading span tables

how do i work out the required size of joist based on the span tables.

assuming i am using 600mm spans and require a 7m span.

do the span tables apply to only a single span of wood, or can you join up smaller pieces and still get the same result

ie if the span table says...

38 x 170 for 600mm centers = 2.69m

does this mean i can use multiples of this?

ie if i need 7 meters can i use 3 x 2.69mm spans overlapped and joined together. would this still satifsy the span table loading.

im assuming NOT as that doesnt make sense to me, otherwise you could join up lots of the smallest sizes together.
So how do i work it out properly to cover 7m span?

the longest table span i can see is 4.64?


edit:has anybody seen JJI Joists, run up to 15m. cant find any prices for them anywhere though!

 

[JohnD]

... 7 metres (23 feet) front to back, 4.8 metres (16 feet) wide...

run them the short way

also look for any internal walls you can use for intermediate support.

 

[softyengin]

run them the short way

can i do that? not sure if there is timber frame to sit them on at the sides. also they would need to be over the trusses causing the floor to be quite high, which is no big deal i suppose

ah wait i need smaller length to get them in there, only acces is via the loft, cant get much more than 2/3 metre lengths thru the hole!

 

[JohnD]

you need to clarify in your own mind whether you are willing to pay for a loft that it suitable for light storage, or some space in a self-store warehouse, or a loft conversion that is strong enough to use as a habitable room.

these options are in rising order of cost.

you are not going to get a strong floor without a lot of cost. Are you willing to pay for it? it is not a cheap and easy DIY job as you might have thought at the outset. It would be much easier to build a shed in the garden.

 

[softyengin]

true.

what would you define as a strong floor, i really just want to store the usual stuff up there plus bokes toys etc.. i dont need to store furniture etc so do i really need to go all the way to a loft conversion.

the way i see it is a shed would take up some space in the garden whereas the loft is wasted space that could be put to better use.

if i was to get some quotes of builders, how would i word it?

"something suitable for storage use only, non-habitable space."

 

[big-all]

reading span tables

how do i work out the required size of joist based on the span tables.

assuming i am using 600mm spans and require a 7m span.

do the span tables apply to only a single span of wood, or can you join up smaller pieces and still get the same result

ie if the span table says...

38 x 170 for 600mm centers = 2.69m

does this mean i can use multiples of this?

ie if i need 7 meters can i use 3 x 2.69mm spans overlapped and joined together. would this still satifsy the span table loading.

im assuming NOT as that doesnt make sense to me, otherwise you could join up lots of the smallest sizes together.
So how do i work it out properly to cover 7m span?

the longest table span i can see is 4.64?


edit:has anybody seen JJI Joists, run up to 15m. cant find any prices for them anywhere though!

no the maximum is the maximum span that timber can span at the given loads

to double the length off span you need to increase the timber size to approching 3 times the size

so iff your span needs says 7x2" at 3m you need you will need somthing like 10x4" for a 6m span

 

[Static]

Hmm.. the load/span tables are just guidelines on what can be achived..

They only go upto 4.5m for a reason as the floor becomes like a trampoline after than and you get vibration issues amongst other things.. 7m isnt unachiveable as ive already stated.. just real expensive as most merchants wouldnt supply that kinda size..

Didnt think short dir spanning would work with timber framed construction you have described without some kinda of cranked member which would be interesting to say the least..

what would you define as a strong floor, i really just want to store the usual stuff up there plus bokes toys etc.. i dont need to store furniture etc so do i really need to go all the way to a loft conversion.

So your not storing books like your original post.. make up your mind.. anyways your loft is already designed for light storage.. so board it and store and enjoy xmas

 

[softyengin]

hi static, dont get ya? i said peviously

"What i want to do is re-enforce the loft to handle storing lots of books, notes, folders, toys and everything else we can shove up there to create more space within the living areas of the house. "

so quite a lot, i've also got a suitcase full of maternity clothes, and one full of baby clothes, oh its about 20 plastic boxes of books/worksheets!

plus other stuff too! so is that light?

i'm still not certain what i've to do. i want to be able to store lots of small items, nothing super heavy, books arent super heavy are they?

just had a new baby so i really really dont want it to fall down on her. thats why i need to be sure!

it sounds like i need to get something like JJI-Joists put in to be sure

edit: oh Merry Xmas everyone!

 

[chappers]

Either I do some work myself or get somebody in, but it seems relatively 'easy' to do?



so in summary i want to add new floor joists onto the existing timber frame with wood thats more than twice as thick as what I currently have, so should be more than strong enough!

Many thanks for any advice guys...

Seriously, what you are considering is not easy work, have you even considered how you will get 7m timbers up there and fitted, it's roof off time and if you are thinking of doing that then consider doing a full or partial conversion.

So far JohnD has given you the best solution and that is get a decent shed or maybe rent a garage from your local council.