You are right about many things. I don't flee because the point of this property isn't the house. Still, I don't want it to fail, and I want my insulation! That will be enough to satisfy my requirements.
Having got poor professional advice and also poor workmanship in the past has made me cautious and cynical, and very careful to be satisfied that solutions will work, and not cause more damage than they fix. This isn't the first time I felt like throwing away an engineered design. One thing I have become clear on, is that whatever goes wrong regardless of the professionals I hire, the cost will likely land squarely on me. Another thing I've learned is that money does not create quality.
I can see the engineer's point, why she likes the mass concrete underpinning model, as it theoretically provides the cheapest and easiest fix, requiring the least teardown of the existing structure. Still, I have yet to believe it will be reliable. I live in expando-land, all clay, no rock. I imagine the constant shrink/swell of the dirt, and I have a good imagination.
I have seen someone do that slow-jacking process you're talking about - it looks/sounds like a really good idea. I was warned NOT to use a hydraulic jack, one must use a screw-type mechanical jack only.
The span between poles is 3.8m, more or less. 3 poles in a line, with 3.8m between them, in 2 wall segments. But this is not in the direction of the main bearers. The wall in question lands on the joists across them.
The place is not constructed like an A, with the roof coming close to the ground (I would call that an A-Frame), it has normal height walls. As you pointed out, the design must, and does have double collar ties on each pair of rafters, to help prevent spread. It has nail plates on both sides of each rafter pair, at the peak. I would rather it had a main ridge beam, but oh well. So the full weight of half the roof lands on the offending wall. The rafters are properly locked in at the wall. The roof has 3x2 purlins on flat, iron on top. No leaks, no rot. One thing about this style of roof - you can usually spot a leak very early. It's not badly built, it is too lightly built (the downstairs fill-in is flat out badly built, probably done by some later damn fool owner).
Before buying, I got poor advice about the condition of the building. Although one can only comment on what one can see, the person I called to look over it performed a pretty weak job, in my opinion.
skin1235,
Jan 28, 4:04pm
good luck, cannot see underpinning as an option, shes read it in a book of some far off land, where buildings are constructed differently to start with and figures a new buzz word that raises eyebrows gets her attention - doesn't do diddly for the homeowner though, and she knows nothing about construction since when do you throw a bit of concrete under a non structural slab and turn it into a weightbearing structure, but shes probably got a degree that lends her advise some creds - wouldn't be happening on any house me or my family was occupying In hard fill clay open a hole 600x600 by at least 800 deep, line the centre of that so its 100 inside the side of the slab, cut a 200mm square out of the side of the slab in the correct place, open the wall and clear for a mechanical jack ( and it may pay to bridge 3 or 4 joists at the top) fill the pile footing with concrete to almost the top of the slab, when cured attach a mechanical jack to it and after finishing the jacking process plaster to bring the level back to the slab level, re-finish the wall Not sure re the insulation, whats in view when you look up, cos it reads like exposed purlons and visible iron?, unusual for any chalet style, even half chalet unless this was originally a shed before becoming a dwelling - I can imagine it would be blardy hot if its exposed iron
Most chalet style do hold heat, and to alleviate that they often have large windows as high up as they can get them, once they are open they create a draft and cool the place down quickly
mrfxit,
Jan 28, 4:46pm
Skin1235 comments are the only 1's that make sense. Slab not built to support large loads, so that has to be bypassed totally. How is a different matter & fully depends on the specific job (access/ depth of pile drillings etc etc) Personally, I would set the support post for adjustment (after settling period) at the top, but again depends on access type. That way you are only adjusting the top AND you are looking at the top to see the changes rather then adjusting the bottom & checking the top, (back & forth till correct)
bcohen,
Jan 29, 1:32pm
OMG you totally pinned it! Whoopie! I'm gonna etch your name in the concrete for posterity. Thank you for your help! Finally, now I can move forward!
The engineer drew holes like what you said, inset the center by 100 like you said. All the calculations for it are there. The big important difference is, she attached the slab to it, instead of notching the slab, and allowing the poles to be independent.
The chalet isn't that rough, not like a warehouse. I bet it probably was a shed originally, but it has ply above the rafters, roofing paper on top of that, purlins on flat on top of that, and then the iron. That makes at least some air gap. When you look up you see the plywood. The walls are insulated, but the roof is not.
Some years ago I had a different chalet, and I put an openable skylight in it, near the ridge. I'd open it all night, then in the morning I'd close it for the day. That helped alot. Here, I haven't yet sought out anyone I trust to do a not-leaky job.
I do seem to have great luck in finding people who fall a bit short of the mark.
bcohen,
Jan 29, 1:47pm
I can see the convenience of that. I've seen videos of people building a stable frame to set their jack into, up higher instead of on the floor. I will think on that.
Sorry bout the duplicate messages. Internet blips.
skin1235,
Jan 29, 5:54pm
I'd probably put 3 squares of 12mm rebar in the hole, and a rebar post in each corner to keep them in position, say 350mm squares 100 up from bottom, 100 mm down from top, the middle one can go roughly in the middle check how deep the flange s on the jack you intend to use and finish the footing twice that below the slab top - once it is cured you can dynabolt the flange down and it will leave a good depth for the plaster cover to reinstate floor level - paint the cut surface of the slab and the exposed underneath surface of the slab with PVE glue a couple of times before filling the notch, you are not going to be able to install a water barrier between the soil and the slab, but if when making the plaster you include a cup of PVA Glue it will render the plaster impervious to water ingress and capillarity The whole thing is not going to be a weekend job, the footings will have to cure for at least a month before loading them up, preferably 2 months ( and if you are mixing the concrete yourself onsite for feks sake don't scimp on the cement, more is better, a 17mpa footing is about as useful as tits on a bull, aim for at least 30, then throw a bit more in), I'm currently laying 3400 sq mts of 40 mpa and am still not 100% confident it will be strong enough for the intended loadings - but the engineer thinks it should be strong enough, now all I have to do is get him to commit that to paper and sign it, lol
skin1235,
Jan 29, 6:19pm
also getting decent strut jacks is near impossible nowadays unless you have mates in the mining industry - but a good workaround is get the adjustable foot they sell for scaffolding, increase the plate size if you think it needs it, and buy some heavy wall pipe to fit above it, cut it to length ( put a robust plate on the top too), grease the threads well and start cranking, will outlast the pyramids
skin1235,
Jan 29, 6:32pm
"The chalet isn't that rough, not like a warehouse. I bet it probably was a shed originally, but it has ply above the rafters, roofing paper on top of that, purlins on flat on top of that, and then the iron. That makes at least some air gap. When you look up you see the plywood. The walls are insulated, but the roof is not. "
I can picture that setup - and its been done wrong - what you have is several moisture traps down the roof, and no air movement They should have started with 3x2 on the flat hanging straight down from the ridge, then put the 3x2 purlons across those, ( continuous air gap from top to bottom beneath the purlons), then the building paper, then the iron - the building paper should be against the iron to facilitate condensation drainage - so think about where that is to dump its wet load ie not onto the top of the walls ( insulation can be fitted in the resulting100mm gap between the ply and the building paper) Your current setup has nowhere for condensation to drain away, and there will be heaps of that - fekin cold in winter too I'll bet if you unscrew a sheet of iron you will find all the purlons have wet uphill edge, and probably starting to eat into the plywood
mrcat1,
Jan 29, 11:09pm
I cant be bothered reading all the other replies, can you put the support beams on the outside of the wall? I have done dry packing on bridge abutments, not a big job.
I have done a house where I drilled bored piles in hard against the house, poured the piles and then put jacking plates on the outside of the base strip footing and jacked a two storey rectangle concrete and brick house back up 235mm on one half of the house.
bcohen,
Jan 30, 2:36pm
I don't suppose you wanna come up North and do this job, when you're done down there?
bcohen,
Jan 30, 2:45pm
I get what you're saying, I can see the problem in my mind. I know for sure that the purlins were laid across, however, there is a second layer of roofing paper on top of the purlins, I forgot about that. I saw it when some roofing was replaced. Plus you can tell when you get up there on a ladder for cleaning the gutters. There's definitely paper under the iron. Oddly, it seems to have followed the standard of the day.
When I had part of it open, I remember being surprised that it was in good condition.
bcohen,
Jan 30, 2:51pm
That's an interesting idea. When you got done with getting the place jacked up, how did you finish off the supports? Were they still on the outside of the house? Did you make an architectural style of them?
235mm on half the house? I can't even imagine what that house must've looked like, needing that! Makes my measly 10mm into nothing at all! (I'm not doing this work to level by 10mm, btw. It just happens that I have the opportunity to level it, at the same time as the other work)
mutation,
Jan 30, 6:25pm
Hi bcohen, Ive been readng this thread with interest. I went about sorting out a sagging beam above our garage door, span 4.2meters, sag was about 12-15 mm. Our engineered solution was bolting a 200mm C-section beam to the back of the beam, whilst it was jacked. We jacked it up 15mm with an acro-prop, and it re-settled back down around half that once the job was finished. But that was expected to happen (residual deflection). It has stopped our doors jamming and arrested further 'sag' or long-term creep as it is properly termed. One thing I was warned about though, which I noted has not been mentioned, is that once the beam has sagged, it is difficult , if not impossible, to un-sag it. I guess it depends on the dimensions of the wooden beam, density etc. In our case, we suspect the creep was due to some moisture getting in, combined with 25 years loading, the beam(s) sagged as a result. Just a thought. I guess it all depends on what amount of sag you are prepared to live with VS cost to remedy. Obviously it isnt going to come crashing down at any moment, but seems like ours was - OK for its day, but for todays standards there would be a steel RSJ there etc.
bcohen,
Jan 31, 10:39am
I'm glad to know I'm not alone in having a situation like this. What dimension was the sagging timber header that you jacked up? With yours you must have had knowledge of the support the rest of the house could provide, for the steel you put in. This job would be alot more complex if I had to span a garage door!
You used an acrow prop for jacking? I was reading online a warning saying "not for house jacking". Are there different types?
I got word back from the engineer already, she has ok'd the method that skin1235 as proposed. *whew, relief*.
trade4us2,
Jan 31, 12:26pm
My house had sagged 600mm around three sides as the wooden piles had mostly rotted away. It was quite weird walking up the slope in the bedrooms. I paid to have the house reblocked. I made a laminated 6m beam for the upstairs. I made it curve upwards, and when put in place it was straight. The building inspector made me have it tested by an engineer, and of course it passed easily. I have just finished replacing one of the posts holding my two story deck with roof up. A hydraulic jack made it very easy.
bcohen,
Feb 1, 7:56am
600mm sag! My mind boggles at the thought!
You MADE the laminated beam? That's impressive! I'd love to know more. What timber did you use, and what glue? What kind of engineer does this kind of testing?
trade4us2,
Feb 1, 9:43am
The house was built over 150 years ago. My architect suggested that I could make the beam (6000x320x90mm) since I built half of the major renovations on the house. I used Douglas Fir and Resorcinol glue and had lots of clamps. After it was installed the building inspector wanted an engineer's certificate for it. The engineer who designed the beam measured the deflection of the beam as we hung up to 1.5 tonnes on it. It deflected by only a few mm. Including the certificate, the beam cost half the price of a commercially made beam (not including the delivery cost). Then the engineer said that he could have designed the roof a different way so a beam was not necessary.
mutation,
Feb 1, 10:08am
Hi yes an acro prop was used, for better or worse. I don't know what types there are, it did the job quite well. I think our sagging beams were around 350x50 (2 qty, back to back from memory) . New supports for the beam were made, attaching to the original structure, one was incorporated into an existing wall by knocking out the dwangs, new timber installed etc. End supports transferred the load directly down to the existing (load bearing) concrete slab foundation, so its only supporting the load that was there anyway, not additional weight and renovations etc. Whole job took 12hours with myself assisting. Glad to hear a more sensible solution has been accepted by your engineer.
pauldw,
Feb 1, 11:32am
Instead of risking the slab cracking at the base of the support the OP cuts the slab. From the sound of it the underpinning in the 2 options is the same.
OP "The span between poles is 3.8m, more or less. 3 poles in a line, with 3.8m between them, in 2 wall segments. But this is not in the direction of the main bearers. The wall in question lands on the joists across them."
Just for clarity is this 2 x 3.8m or a wall 3.8m long supported on joists spanning 1.9m?
bcohen,
Feb 3, 7:34am
Thank you for that! Can you tell me, where did you source your Douglas Fir from?
I want to fabricate a main beam for a long narrow workshed for ripping timber. I can use this info!
I hope the beam was exposed, so you got some pretty out of it, too. Then you could be less annoyed that your engineer said that, afterward.
bcohen,
Feb 3, 7:43am
It's 2 sections, each of which have a span of 3.8m give or take. 1.9 if only haha!
You are right, the underpinning is the same either way. What I can't understand is, why the engineer rejected this the first time round, when she's accepted it now. This is what I pushed for in the first place. All I can think is, people are people, and hear what you say through a filter of their own understanding. When I asked for this, she must have pictured something else. All I can say now is that at least it came without a monetary cost, though it caused me alot of stress. I've done alot of research on underpinnings and gone through alot of statistics on success rates and failure modes. So I guess I'm smarter. And more cynical.
Maybe it's because this time, I used the language of skin1235. I initally talked about drilling a hole for an independent pile through the concrete, whereas he talked about cutting a notch. How you express something can make a difference, eh?
trade4us2,
Feb 3, 8:22am
The Douglas Fir came from Warehouse Building Supplies in Henderson. It was cheaper ($1.50/m) than H1 pine, and the builders said they would rather not cut treated timber. My roof is a double gable (W shape), and some diagonal timber would have held it up instead of needing a beam. I suspect the architect drew a beam, so the engineer designed one. If the timber you get is shorter than the beam, you need to make the joins at a very sharp angle, i.e. much sharper than 45 degrees.
Why not have your beam going across the shed instead of lengthways? My beam is exposed, so I can see if it starts falling apart, which it hasn't done for 25 years.
pauldw,
Jan 3, 1:02am
I guess doing it without cutting would have meant less disturbance in the room inside the wall. You are providing more support for the joist(s) under the wall, what about the rest of the room, does the floor show any bounce? AFAIK the original pole structure should have been an engineered design to get approval.
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