Breeze Blocks Or Lightweight Aerated Cement Blocks

[annieigma]

Any builder chaps out there know what weight a lightweight block building can take? its a single floor building, attached at one end of the house to another added brickbuilt extension. we removed the flat roof, and find that the walls are single skin with battens and plasterboard inner, render on the outside. roof area is 3.5 mtrs long and 3 mtrs wall to gutter on slope. thinking of putting two 5x2 inch beams from the corner to the existing brick built wall at the front, cutting into the bricks at 300mm so giving the beam support at both ends across the patio doors, similar down the side attached to the main house wall, then single 5x2's from house to front to support tiles ( redland 49). I have recounted the tiles on the existing extension and it will need 150 tiles to cover the area at the same spacings. i posted about this some time ago, and we bought 800 secondhand tiles, but just started work this week
thank you for any help..

[Zacs-Master]

Annie, I've reported this in the hope that TheBuilder sees it. Not sure why you're cutting into the brickwork instead if using joist hangers and you don't say whether the single skin block wall has any columns / piers in it along the 3.5m length for stability.

[Zacs-Master]

Re posted not reported.

[The Builder]

Thanks to Zacs for the nudge. :o)

I remember this, Annie. Am I right in saying the patio doors will be directly under the eaves (guttering level)?

If so, it will depend on the width of the doors you're using. 1800mm ? 2400mm ?

[The Builder]

Loadbearing won't be a problem for the masonry. Bricks; dense concrete blocks; aerated con. blocks; all of them are made to take much more than the loads you'll have in place.

Load is transferred vertically to the foundations. This is the only unknown quantity here. I can't do more than assume the existing foundations are good.

I ask about the patio door width simply to decide the beam sizing.

[annieigma]

Thanks all of you, the doors are 2200, butting up to a brick wall one end, and at the other end they fix to a course of blocks which are the start of the corner, so have one and a half blocks for support.

thank you, annie.

[The Builder]

Annie, for a span of 2200mm, and an unsupported rafter length of 3000mm, the minimum size for an eaves beam is around 9x2. Two 5x2s fixed together would be at least as good, maybe better.

Make sure the 5x2s are either bolted together, or very well nailed together.

If you're having ceiling joists, then have them run from patio doors to the building (same as the rafters.) This will give lateral restraint to the patio door wall. This is to prevent the load from the tiles pushing the front wall out.

[annieigma]

Thanks the builder, existing ceiling joists go from the other direction. could we, instead of removing them and putting new ones in, put noggins in ( would this work)? or lay something like 5x2 " timbers from house wall to new timber across patio doors and nail them to all the joists, therefore giving added strength to the new patio joist? I do see your point about the roof pushing the patio doors outwards, but looking for an easier option than taking the whole lot down, which then means the timbers will be no good as too short to go in the other direction. Do greatly appreciate your advice, thank you once again.
Annie.

[The Builder]

Yes, use the existing joists. See if you can get just two of these from a builders' merchants............

http://www.screwfix.com/p/heavy-duty-restraint-straps-1200-x-150mm-pack-of-10/74769

Put noggins between the joists where the straps sit, to prevent the straps bending the joists.

Position the straps at two points roughly dividing the width into three spaces. Does that make sense?

[The Builder]

.............. nail them either on top or under the ceiling joists... depending on how they line up with the eaves beam. Hook over the eaves beam and nail to it.

[annieigma]

Hi The builder,
Yes makes good sense. there is a travis perkins, jewson and a wickes here, so should be able to get straps from them. Just had a look at the waether forecast, heavy rain here from midday tomorrow for a day or so, now got to try to make the room weatherproof as there is no roof on at all, more fun.
thanks for all your help,
annie.

[annieigma]

question for the builder ( can i send you some money for your advice?) we are continuing the tiles from the existing roof, which were cemented and overhung to finish that roof off. do we need to knock all the cement off and remove the tiles, and interlock ours as a continuous roof, or is there some way of waterproofing a bridge between the existing and the new.? looks like a couple of days of fine weather next week, so aiming to get the job sorted.

[buildersmate]

No doubt my boss will be along with his definitive answer, but my view is the job would be far better by scrapping the verge end tiles that have mortar on the edges by ripping them off, and interlocking the the new into the old. You won't have a sealing issue to solve then.

[The Builder]

Haha, Boss?. Teamwork BM :o)))

Yes of course, BM is quite right. There are perfectly good ways of butting up to the originals with a waterproof joint, but only as a last resort. It's done where two houses abut, and you don't want to interfere with next door. Some people (quite illogically) can be fussy about these things.

The good way is most definitely to remove the verge tiles and replace them with ordinary ones. Then run the new roof into the old. Since you have concrete tiles, verge tiles will have a blank on one end (no interlock). Ordinary ones have the overlapping interlock on both sides... one under, and one over.

No payment needed here, Annie. There's a whole load of us glad to help.

Actually, it does happen in real life. People do often offer to pay when I help them out. My usual answer is to have them drop a fiver into their favourite charity box ;o)))

[annieigma]

Dear Mr. the builder, the advice i need will take more than a fiver into the charity box, in fact, if you can help me out further, name your charity and i will put £20 into it and send you the receipt.
thank you, annie.

[The Builder]

Ok Annie. You're on :o)))

Hope you don't mind that it's a charity local to me here in Devon. Staffed by volunteers, many of whom I know well. Have done loads of free gigs for them in the past with my band. Kind of a drop-in and support centre for cancer sufferers and their families...........

http://forcecancercharity.co.uk/

[annieigma]

Hi the builder, £20 donated to force in exeter, they are sending me a letter of confirmation and getting an extra £4 tax relief. Ordered the lead flashing and sarking, now, here we go again, fixing the rafters to the house wall, is it a wall plate or joist hangers, and as there is a degree of X? slope, what happens? do we cut the rafters at the prescribed angle? i assume we are trying to add more restraint to the front wall, using the house wall as an added anchor?
thanks,
Annie.

[The Builder]

Well done Annie. Thank you for that. I promise you it's a great cause.

Right, lateral restraint. Since you'll have restraint from your ceiling joists and galvanised straps, added mechanical ties are not usually necessary at rafter level.

That itself will give a surprisingly good restraint... especially in conjunction with the strapped ceiling joists.

Not joist hangers. They're for horizontal applications. A 6 or 7 x 2 plate fixed to the wall at rafter level (sometimes known as a "wall-piece"). Fix with "rawlbolts"; "fischer bolts" or similar.

Then make a top-cut to each rafter. With a right-angled triangle, this angle is just the result of subtracting the pitch from 90 degrees.

Skew-nailing is all that's needed to fix them. (100mm nails driven in the sides at 45 degrees to the rafter.)

[The Builder]

//// That itself will give a surprisingly good restraint... especially in conjunction with the strapped ceiling joists. /////

My paragraphs are wandering around today. That should have been at the end.

[annieigma]

Hi The builder,

Can you please tell me what size rawlbolts would do the job, we are using a 6 x 2 wall plate, found lots of different ones on screwfix, but don.t know which ones would be substantial enough.. Next problem we have just found is that the 6x 2 eaves beam will raise the tiles 4 higher than the existing roof line of tiles which we are bonding into, so, if we were to support the roof rafters with another beam several inches back ( this would be supported by a wall either side ),( this would give us the correct angle ) could we then cut notches into the eaves beam for the rafters? This would be more for closing the roof than weight bearing.
thanks again for your help,
annie.