workshop loft support

[mynamehere]

Hi guys,

New member to the forum here!
I've been looking around on this forum for a couple of months and picking up tons tips and tricks (thanks everybody!)

I've been lucky enough to get my hands my neighbors stone built outbuilding (4,8X5 meters internally) with a pitched slate roof, until now this was only inhabited by the local swallows and perhaps some pigeons, in its previous life it must have been a stable.

I am going to convert this space into a workshop and want to incorporate a loft for storage.
I don't want any support from the floor as this would be in my and my tools way.

My question would be, is it possible to "hang" a loft floor from the existing rafters?
Would I have to install an RSJ?
The roof at the moment consists of a ridge beam and rafters, all supported by single skin (thick) walls.

Thanks for any tips!

Ferenc

 

[LancsRick]

What are the current rafters like and how are they supported?

 

[mynamehere]

The rafters are 2x4 if I'm not mistaking supported by the ridge beam and 2 purlins (10X2?)
The ridge beam and purlins are supported by a single skin block wall one one side and a solid stone wall on the other.
The bottoms of the rafters are sitting on top of solid stone walls.

Or is that not what you meant?

 

[Woody2Shoes]

I think you'd be much better off taking professional advice from a structural engineer. There are too many unknowns (e.g. do you know how the substructure is made?) and the consequences of a cockup are potentially very large.

Most roofs are not designed to subsequently have a floor dangled off them and the walls may not be suitable either.

I suspect that the likely most cost effective solution may be some kind of steel skeleton with columns sitting on the floor, with beams across which timber floor joists would sit - but only an SE can tell you for sure.

Cheers, W2S

 

[sunnybob]

If its old and has been abandoned, you can bet those roof timbers are only half as strong as you think they are.

Dont hang any serious weight up there.

 

[Woody2Shoes]

This is the kind of thing I had in mind:

https://www.mezzanine.co.uk/productsystem/

https://www.invictamezzaninefloors.co.u ... ine-floors

 

[MikeG.]

Hi and welcome.

You can span 4.8m from plate to plate without any involvement with the roof. However, this will depend on the roof plates being high enough to give you adequate headroom. If you do decide to do this, I suggest 225x65 joists at 400 centres, given that you want to use this for storage. There is a structural engineer or two on here, so you might wait for them to confirm those timber sizes, but I'll have a little 5p bet with you that I've got it right. (I'm an architect).

 

[mynamehere]

Thanks for the replies!

The building wasn't abandoned, just not used, the roof structure looks very sound as well.
The 2 purlins are 10X4, the ridge beam is 9X3, the rafters are 3X2,5 at 16" centers.

I want to put an insulated floating chipboard t&g floor in, as others have done on this forum.
From the top of the concrete floor to the top of the walls where the rafters sit on is 2,4 meters, I want to keep enough height for a full sheet, so that would mean fitting the loft floor higher than the top of the walls.
That's how the "hanging from the roof " idea came about.

I might go with something like what Sunnybob suggested but made out of timber and maybe only half of the garage,.
If I would go with Mike's idea, could I hang the floor beams from the end walls either side with metal brackets?

Cheers!

Ferenc

 

[MikeG.]

No, you couldn't. At least, not using timber.

Those roof timbers, never minding their condition, are not big enough to support a storage floor. You can use my suggestion, put in some steel supports, or build a new roof. That's pretty much your set of choices.

 

[Sawdust=manglitter]

Only skimmed this post (as i'm in work) so I'll try to have a better read of this post when i get a chance tonight, but for now take a look at the below post regarding proposed loading. And in terms of hanging the floor from existing rafters that would be a big no-no unfortunately.

post1153512.html?hilit=mezzanine#p1153387

 

[Sawdust=manglitter]

I’ve done countless surveys of old barns to accompany planning applications. For domestic conversion we usually end up recommending the replacement of the roof structure as the existing roof (min. 30yrs old partially exposed to the elements), even if no sign of deformation, would usually never be proven by calcs to current standards. So that gives you an idea that you shouldn’t add any additional load to the roof, even boarding and insulating the roof may be very dodgy. So to start with you won’t be able to hang any structure from the roof. But you could replace the existing roof with suitably designed attic trusses?

So the next option, as suggested by Mike, to install floor joists between walls. It would completely depend on what you plan to store up there and how it may be used in future. Standard domestic floor loading is designed for 1.5kN/m2, which equates to 150kg/m2, which is not actually that much if you work out the weight of wood, as I said in the link in my reply above. If you were to buy a bulk of oak boards which were 8x1” boards and they were stacked up to a height of say 1m, them that equates to approx 160kg/m, so that means your already over the standard domestic loading and that’s not accounting for anything else you may have within 1m of this stack of boards. So looking at the standard floor joist span tables for your case would be a no-go as they are for domestic loading only. But saying that a structural engineer could certainly design you floor joists for any increased loading, but they you’re faced with the issue of how to support them.

Completely depending on the condition of the walls, but there’s maybe a possibility of installing a timber wall-plate to the face of the side walls with chemical anchors and then hanging the joists from proprietary joist hangers, but then you’d have reduced headroom. But maybe you could do this higher up between the gable walls (spanning same direction as the ridge beam and purlins)? And if required, to reduce the size/cost of the joists you could install a suitably designed steel beam at half way spanning perpendicular to the joists (including padstones)? So then you’d have increased headroom apart from a downstand where the beam is only? But if there are any door or window openings underneath any additional loading them the adequacy of these would need to be checked by the SE.

If going for a timber frame or steel frame structure inside to support the joists then you would need to be aware of installing foundations for the posts, and also be aware of the fact that old stone buildings don’t tend to have any foundations and the walls are quite shallow below ground, so digging new pad foundations for the frame structure would possibly undermine the existing walls, so you may even then need to underpin the existing walls locally. But again, a SE would advise you on that and be able to design you the frame.

Whatever you end up doing I would recommend contacting a structural engineer and get them out to have a look.

Anything is do-able, depending on budget. And I wouldn’t want you do do anything potentially dangerous. Hope this is not too off-putting. Good luck

 

[mynamehere]

Thanks for the extensive explanation and tips, it's very much appreciated.

I've already given up on the "hanging from the roof" idea thanks to the wiser people on here.
So here is what I'm planning to do now...

I don't want to lose any height (stay above 8') so the bottom of the joists will be slightly above the bottom of the roof.
The walls to the neighboring garages are concrete block on one side and 18" stone on the other.
If I would hang 10X4" timbers along the length of these walls and attach them with M16 threaded bars drilled through the walls with 4X4" steel plates for washers (I'm sure the neighbors won't mind...) I could then span the remaining 4,5 meters with 10X3 or 10X4 joists on 400MM centers hanging in suitable hangers.
For added strength/security I could support the 2 wall timbers on the corners and the middle with 10X4" timbers as well. (the concrete floor is 8" thick)
This would leave me with not much more than a crawling space for a loft but it's only for storing relatively light stuff (Christmas decorations, boxes of clothes, ornaments etc.)
The total load on the floor is never going to exceed 250-300kgs.

Does this cunning plan still sound foolish or too risky?

Cheers,

Ferenc