Doing without a ceiling

[David]

After several years being blissfully forgetful of the ways of tradesmen and the interior of Wickes, we are about to embark on another relationship-enh ancing building project in our new house. We plan to knock a few internal w alls out and add a two-storey extension to give us a third bedroom and a di ning room. The extension will have a pitched roof to match that of the mai n part of the house, It will be set back a little way and the roofline wil l be slightly lower. it will be about 10' wide with the wall of the existin g house on one side and its own gable end on the other.

Is there any reason why we should not do without a ceiling in the bedroom a nd just have a pitched insulated roof? My reason for asking is that the ar chitect poopood the idea out of hand as he said it would not be stable. Sur ely the beam at the apex and the purlins would be sufficient to tie in the top part of the gable end. I presume we would we need a beam running from f ront to back to support the roof and prevent it splaying? Is it thoroughly obvious I don't know what I'm on about? Has anybody any experience of doin g this? All suggestions welcome.

David

[Cash]

You will need to have the bottoms of the rafters (at wallplate level) 'tied' to its opposite rafter with ceiling joists across the span of the room to prevent the weight of the roof pushing down and spreading the rafters off the wallplates. The rafters are fixed simply by putting a plumb and seat cut at the bottom onto the wallplate and then simpy skew nailed into the wallplate.

Also, depending on size and materials, that little lot can weigh around 20 tons or so - and that doesn't include the weight of a heanvy fall of snow.

I would suggest that you take the architects advice - and if you insist on having an 'open' roof space, then he can design the roof so that the rafters are tied at a higher level. Either way they need tying.

Have you also though about the extra expense of heating that void above your head?

Cash

[spuorgelgoog]

It's certainly *possible*. However some engineering will be required to sto p the walls spreading apart. A structural engineer would advise.

Instead of being open to the apex you might consider a coombed ceiling i.e. part slope and a horizontal ceiling partway up. This would give you more h eadroom but without losing heat to the apex. The slopey sides might have ve lux type windows in for light and privacy or have mini dormers.

Owain

[Tough Guy no. 1265]

o stop the walls spreading apart. A structural engineer would advise.

i.e. part slope and a horizontal ceiling partway up. This would give yo= u more headroom but without losing heat to the apex. The slopey sides mi= ght have velux type windows in for light and privacy or have mini dormer= s.

What's wrong with having the ties higher up?

-- =

If you own a =A33,000 machine gun and a =A35,000 rocket launcher, but yo= u can't afford shoes, you may be a Muslim.

[Lobster]

On 08 Mar 2015, [e-mail] grunted:

Somebody (IIRC Adam?) posted a brilliant set of photos here a few months ago, where someone had done just that on a single-storey building, with exactly that effect...

[Chris French]

In message , Cash

[stuart noble]

Yes. Pretty funny as I recall

[Andrew Mawson]

It certainly can be done, and is done for instance in 'portal frame' barns, where the steels join at a bolted plate at the apex, and are webbed at gutter level.

Expensive in materials and professional fees.

Andrew

[Nightjar]

[Tim Lamb]

In message , Chris French writes

[Brian Gaff]

I was just thinking tthe same, in Churches where you often get open to roof expances you also get external buttressing to stop the splaying effect as well as other systems to stabilise the construction.

I was in an extension once with a design similar to the one mentioned, but it had a ceiling at least 3 quarters of the way, with a very steep laddr/staircase at the gable end with a window, and landing and a door into the roofspace. I never saw what was in there but it had no windows, so was probably storage only. Of course this would only work if the height was there.

Brian

[The Natural Philosopher]

In my house we achieved it by using the top storey floor joists to tie the walls together. And then using only part of the pitched roof - there were ceiling joists to tie the rafter CENTRES together, but the lower edges of the rafters were not constrained at all except by being notched into the wall top.

[Mike Barnes]

We had something like that retrofitted. There are two purlins on each side. One is wooden and original, the other steel and fitted as part of the conversion. It was all designed by a structural engineer, and according to the builder, totally over the top strength-wise.

One unexpected minor drawback is the noise from rain and from pigeons dancing on the roof. But the room has a real spacious feel that more than makes up for those little problems.

[fred]

In article , Mike Barnes writes

That's a lot less intrusive than some I've seen and the purlins look quite characterful. Looks like you have quite a span too so the timbers don't look oversized (even allowing for the hidden part).

I'm not entirely sure I agree with the suggestions that the entire wall perimeter needs to be tied too aggressively. If there is a hefty steel supporting the apex then the load expressed by the joist ends should be vertically downwards so I don't see the tendency to spread, particularly if a sliding joint were considered on the wall plate instead of a fixed one.

No doubt however there are forces concerned with even a cm or so of sag in the apex steel under full load so I can see the potential for some splaying forces.

IIRC, Adam's anecdotal post was different in that the apex was unsupported and so all the forces resolved into splaying and collapse.

[Mike Barnes]

We like the look. The actual span is 4-4.5 metres (the opposite wall has a dog-leg).

The steel purlins were plasterboarded then skimmed and combed to give a slight woodgrain effect, and stained to match the real wood.

I could look out the drawings and calculations if you're interested.

[David]

Dear Folks

Thanks for all the advice. It's as good here as I remember from the last t ime I lived covered in dust. I've taken away that it *is* possible (though with that builder's phrase "anything is possible, how much money do you ha ve" in the back of my mind). I'll discuss the - high-tied - multi-purlin - central tie solutions with the builder. The heating costs are a consideration, but it' s not going to be *that* high.

Mike - thanks for the offer - I may take you up on it.

Thanks for the other suggestions, but I think even suggesting the hammer be am roof will get me committed. We may not have enough space to the boundar y to permit flying buttresses...

Thanks

David

[fred]

They were so good that I'd missed the mention of steel in your post :-)

I'm not planning anything like this soon so probably no need, more of a general discussion point.

[Fredxxx]

There are perhaps a few good reasons why you shouldn't.

It is possible to rest each side of rafters on two or more purlins. That way there is no sideways force on the wallplates where all the force is vertical in nature.

It's not so much the width of the room, but the length, and the corresponding length of purlins. They might have to be modest RSJs.

Perhaps your architect isn't confident and so he/you'll need to employ a structural engineer to produce plans.

[ARW]

The photos are still there.

I was there again on Sunday. The lighting now will have two LED strip lights sat in a trough at eaither side to uplight the ceiling. No idea if it will work as I have never seen or tried this before.

[spuorgelgoog]

It might look quite nice. :-)

Critical thing is to get even illumination along the length, and a nice gradual brightness change as you look up the ceiling.

Owain