Demolitions and propping for your home extension…… all you need to know.. how to do it 

Thank you for your comment. Really appreciated.

Thanks and best of luck with your project

Thanks for comment. Yes, the money you can save on this part of a build is a lot, you just need to be well prepared. I totally agree that it’s so satisfying to do this part of the project yourself.

Same for me in my loft. I ended up hiring a team of lifters to get the beams up into the loft, did the prep work before: padstones in all to SE spec, then the guys just got them up for me and dropped them into position, took them less than 30 minutes. Had to knock holes in the wall to push the beams through but after I just bricked everything up. The entire job cost me less than a grand including all the steel, padstones, lifters and SE visit and report. Cheapest quote I had was £3k just to fit them.

How much did you save by doing it yourself?

I trained as an architect, and I think you could probably say the same about me when I graduated. It’s definitely true that some of us never get on site, spend the whole time just drawing, and then you get a bit of a disconnect between the real world .

Thanks a lot

Thank you too.

There is no “formal” qualification for doing demolitions and propping. I don’t have any anything to show them. Insurance companies and their loss adjusters are looking for the appropriate due diligence and following the engineering specifications, if an accident occurred. An example of your insurance not paying out is through you using the wrong type of props, or the wrong positioning of props, or not having evidence of having made a method statement. If you can demonstrate competency, through your previous years work, they would have to insure you, just like they’re insuring all general purpose builders. I always tell them what my job is, what they need from me, and whether I have cover. If they still won’t, get a different insurer. Thanks a lot for your comment and best of luck.

As long as the ground is level and well compacted with boulder clay or similar residing near the surface, so no loose topsoil, scaffold boards are ok. But the boards must be level and secured. Don’t worry about the concrete. Write your step by step method statement and safety plan, then finalise with your structural engineer. Key thing is to have everything rigid and tensioned without being too much to damage the existing walls, because even a few millimetres of movement will cause you problems. But…as I said…check all with engineer once you’re prepared and before you start.

I used a primed (painted) 254 x 254 x 89 steel i section for the beam, sitting on 203 x 203 x 72 columns at each end. But I had to splice the beam into three parts to fit it in, as it was too big. I made a video here about how I did it, and how a splice works. Don’t forget to get all your sizes checked by engineer. Steel beams for house extension - working with structural engineer ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-O-yt3P6JL90.html

It may have been galvanised…I can’t recall

@@build-better-things thanks so much

The problem with your weather barrier idea is that water may still get in, further up the wall. The correct way to do it in your situation is to use a plastic preformed cavity tray which comes in short sections. You go along the course above the roof abutment carefully knocking one or two bricks out and exposing the inner leaf. You then fit your cavity tray pieces, which interlock with each other horizontally. You then add back in the bricks, and move along horizontally and rinse and repeat, weep holes as you go. Your flashing onto the roof then laps over the lower horizontal leg of the tray. It’s hard to describe. Hope that is clear.

@@build-better-things Awesome, I had a feeling you would know! Very helpful.

It’s not the length of the opening that determines it, it’s what the load or weight over the opening. For a two storey opening such as the example I’m showing, the loads are such that you would never, ever, use strong boys. I don’t have the space here to show it using Kilo newtons, but it’s a simple calculation. I’ve seen the same RU-vid videos of so called builders using strong boys, they are clueless and dangerous. The fact that most (not all) get away with it is irrelevant. I’ll consider strong boys on single storey openings for example.

Thank you, for thr reply, videos r really good to watch and appreciated. If strong boys only ever used for single story extensions, it would only be to hold the roof . Thanks again, nice simple easy to follow videos. Wish I'd found them before paying for my planning drawings ha ha . Thank you

You raise a good point. Unfortunately the laws of physics doesn’t care about your bathroom. As far as I know, needles are the only economically feasible way, but your structural engineer might be able to design a splice beam system where you go along horizontally in metre increments inserting the splice as you go, without the need for needles therefore. Probably cost more than the redecorating if your builder does it, but perhaps using a step by step approach , hopefully as I’m describing, a self builder could do a perfect a job, since time and organisation is the main resource for demolitions . Alternatively I guess the trick is to wait until after you’ve done your extension before decorating your upstairs bathroom and bedroom. And, no matter what your builder says, to never use strong boys.

"Unfortunately the laws of physics doesn’t care about your bathroom" That you are right. I have been researching for about a year now to get the courage to do my own extension, but I think i'll leave this part to someone with experience and will take your advice to only use the needle goalpost system. It's only a few tiles and a bit of plaster to replace. It's just looks more chaotic than it is I guess. Thanks for your videos

Thanks for taking the time to comment. Best of luck for whatever way you decide and feel free to ask if you have more questions