So how do I make this ceiling then?

[David Pearson]

G'day.

Eventually I will start this project instead of just worrying about it here!

I have this nice new roof on a single-storey extension, and no ceiling (pulled it down and chucked it away).

Here is my plan, I would be grateful for advice and criticism....

The room is 2.5 m x 4.0 m, with a roof that drops 80 cm from one end to the other (i.e. 80cm in 4.0 m, making the roof roughly 4.08 m long, measured along its length, inside).

Put a 2.5 m wall plate at each end (one low, one high), hang 4.1 m rafters/joists at 60 cm centres. Rafters to be deep enough accomodate 130m insulation (statutory to achieve 0.2 U-value), then battens and noggins below the rafters for the plasterboard.

This ceiling is not to support anything but itself and its insulation.

(An alternative, which is a flat and level ceiling, is not acceptable because the low end is too low.

Another alternative would be to use long wall-plates and short joists (across the room), but there are structural irregularities that would make this difficult. Virtually impossible for me!)

Is this plan any use? If so, are there building regs that it needs to comply with? What sizes of timber do I need for the wall plates and rafters/joists?

Thanks very much! David Pearson

[BigWallop]

If it's just a flat level ceiling you want, then why not go for a suspended one. These are light weight, but strong enough to support lagging for the U value requirements. They're also strong enough to hang lighting in and on them if needs be.

Making a heavy timber structure if it's not really needed is a way to much over engineering, in my opinion anyway, and you'd get away with a light weight suspended ceiling without all that hassle.

[bigcat]

how do you make those then?

NT

[David Pearson]

Thanks Big Wallop, but I cannot have a flat level ceiling because the low end of the roof is too low to allow that. I am not tall, but the low end is still a bit close to my head.

Can a suspended ceiling be done on a slope? The hangars would have to be vertical but not perpendicular to the rafters. Can it be mastic'd to the wall to prevent heat loss through air movement?

Thanks, David P.

[BigWallop]

Are the roof beams on an angle as well? You could place the flat part of the suspended ceiling at a good height for the room, remembering that the minimum height for a ceiling is 2,400 mm (2.4 mtrs), and the lower part of the beams can be plaster-boarded on the angle to hide the rest of them. Or you could just plaster-board across the original beams themselves, instead of dropping the height any more.

A suspended ceiling can be as simple as lengths of timber fixed to wire or timber hangers fixed from the beams. Light-Weight timber can be 25 mm X 50 mm lengths just enough to screw plaster-board on to. That's if the ceiling isn't going to take any other weight but its own and some light fittings.

[David Pearson]

The beams, about 4.0 m long, are indeed on an angle. The long axis (about 4 m) of the room runs east-west, the short axis (2.5 m) north-south. The roof drops about

80 cm from the west end (high) to the east end (low), so the roof beams do the same. (There is another room the same size and same orientation in the extension, but I am working one room at a time.)

What I wanted to do was this: put the 130mm (or similar correct value, it is about that size) between the roof beams. And then plasterboard under the insulation and beams. But if I do put insulation between the roof beams (rafters), then the ventilation across-rafters will be blocked. That is why I need a ceiling lower than the roof beams - to install the insulation while leaving ventilation space between the ceiling and tiles.

So it is tiles (and sarking and counter battens and stuff) at the top; rafters below that, with good eaves ventilation but only one tile vent in each room; then I put the new ceiling below the rafters, and attach the insulation, plasterboard and light fittings to the new ceiling.

This sounds ideal, if only I can hang it from my sloping roof, and seal it against the walls for insulation purposes.

Big Wallop, I sure do appreciate your helping out with this advice.

-DP.

[David Pearson]

I missed out the most important word here. Should read:

"What I wanted to do was this: put the 130mm *insulation* (or similar correct value, it is about that size) between the roof beams."

Thanks, Pearson

[Ian Stirling]

Suspended ceilings are the easiest sort to make. "I'll put a ceiling up there soon, really."

[BigWallop]

If the roof beams are that low from the ceiling to floor height, then why not put lagging directly between them? You can then directly plaster-board over the whole thing. No need for a false or suspended ceiling at all, and I'm sure the insulation values would be enough for the size of the rooms. It would also give you loads more head room and let you stretch your arms up in the mornings. :-)

[bigcat]

:)

[David Pearson]

Good morning.

That is what I had hoped to do, but: if I put the insulation between the roof beams, then that will stop the air circulating around between the roof beams.

I have a full-length eaves vent (well, the roof does anyway :) and one tile vent that vents one between-the-beams gap. If I fill all the gaps with insulation (apart from the 50 mm required space at the top), then only that single between-the-beams space will be ventilated. The others will not.

That's why I think I need to have the insulation held up by a separate ceiling completely separate from the roof beams.

Cheers, DP.

[The Natural Philosopher]

The way my BCO expected me to achieve what you have was by using less celotex between the beams than the depth allowed.

I used 75mm on a 100mm depth rafter.

This allows a 25mm airspace over the top.

In my case I also had a void at the ridge - the ceilings were not carried all the way up - and so the ridge vents provided efflux for the whole area.

This is pretty much 'standard practice' for a 'cold roof' with a storey built under the eaves.

I've missed the first part of this thread, but if its possible, and you are attempting what I think you are - insulating and boarding out a loft cavity in a cold roof style house - I would do it this way.

Put some horizontal timbers across the rafters up near the ridge.

Now cut and wedge as much celotex as you can fit between the rafters and between the new horizontals, and tape ultra carefully using the metal tape you buy for this purpose. The tape goes over the joists and onto the celotex. The purpose is to form a complete airtight and moisture tight barrier round the whole place. That stops cold air getting in, and warm moist air getting onto your cold nbeams, condensing and causing rot.

Then simply plasterboard up, paper or skim, and paint.

You have about a 25mm gap above the insulation from the eaves vents to the new tunnel formed by the ridge and the new horizontals and your ridge vents will'exhaust' that. The BCO will be happy, and with all draughts sealed out, so will you.

One caveat: With no way to allow moisture to escape from the living area, the BCO will insist on some kind of background ventilation 'achievable in a secure manner' - usally without opening a window, so you may need to punch holes in walls and use trickle vents etc. to allow fresh air in and sweaty air out.

[David Pearson]

Before I get back on topic... I was thinking of following the BC regs carefully, and therefore did not think I needed to involve a BCO. I will photograph the project as it progresses (if it ever does!) to provide evidence that everything conforms with the regs, in case I get inspected in future.

Is this OK, or do I need to get a BCO in at the start?

Thanks for this, but ... I can't do the same thing. The extension has a lean-to design, so the top of the roof abuts the end-wall of the house, a long way below the house's eaves. It was originally a garage. (There is a whole BCO nightmare there, but that is a separate issue!) So it has no ridge and no ridge-vents.

Instead, it has full-length eaves-vents and two tile-vents. So if I fill up the gaps between the roof-beams (leaving a space below the sarking etc.), then the gap that the tile vent is in (one tile-vent in each room, I am only talking about one room for now) will be ventilated by the eaves-vent and tile-vent, but the others will only be ventilated by the eaves-vent.

So it seems that I can't put the Celotex/whatever between the roof-beams - I need a space that allows the gaps between the roof-beams to "talk to each other".

Thanks again, but this is not the situation. I am just trying to put a ceiling in a one-storey extension, with the regulation amount of insulation (by U-value), having got a new roof on the extension.

I had not though of that one. Maybe this is a good reason to get a BCO in? I can read the regulations, but I might miss stuff that an experienced builder knows about.

Regards, David Pearson.

[BigWallop]

I still think it'd be easier getting something like this

I'd say. So much lighter in weight, and doesn't need any special fitting techniques. Once the plaster-board is up you fill above with your lagging system, and the jobs done. No huge timber weight involved. No humphing and grumphing with timber joists and huge wall fixings. So much easier all the way through.

[David Pearson]

Thanks Professor Wallop and everyone else who has educated me about all these things.

-David P.