supporting block and beam floor with existing wall.

[rssteve]

I require your thoughts please. I am just having piled foundations in a U shape to the rear of my house to add an additional room. The room is 5.1m wide and 3.5m deep. Due to the garden being on top of an approx 4m high embankment, and the extension getting nearer to it than the original house, I went for piles and a ground beam. My initial thought was to support the block and beam floor side to side, I had the option of putting a center beam to split the span up but decided against it as it was an extra £500 and the longer beams needed to span it were only an extra £100 or so. Also less to dig out.

Anyway now I have got to the stage of ordering them I now find out if I want them off loaded its an extra £60 plus the vat and since we live in a cul de sac the artic needs to be a rigid, an extra £100 plus the vat. Bear in mind the original quote was £400 for 11 beams. Not so cheap now.

I've also since been reading that long spans are very bouncy, so my next thought is could I span between the original house wall and the new piled rear wall. The beams are available locally, works out cheaper and will be easier to handle. My only concern is the additional weight on the existing rear wall of the house. House is 1970, foundations are approx 650mm deep and about 600mm wide with some clay present. Is this something I should avoid or should it cause no issues, I worked out that each meter of wall will be supporting approx 350-400kg of additional weight.

thoughts welcome.

 

[noseall]

How were you actually going to lift the beams into place?

We opted for a centre wall even though the foundations for this additional wall needed to be eight feet deep! No brainer when you consider trampolining beams, nightmare access, crane etc. You want manageable floor beams unless you have access to a lot of heavy lifting and moving equipment.

 

[rssteve]

A couple of dollys and man power. The beams were only 180kg 4 people to push them into place on dollys then the final lift 1 end at a time.

The option of a centre wall has now passed as the ground beam is being poured this morning.

Shall I just crack on and support from the original house wall?

 

[tomfe]

What span were you going to do at 180kg, beam 5m? That's long for bnb with no mid span support.
You can cut the beams into the existing house wall, no doubt you'll be taking brick work out and knocking through so the net difference is weight might be zero.
But even not I would have thought they'd be OK. What is your span in this direction?

 

[rssteve]

Supreme beams are 34kg per meter. 5.1m span. They were designed to be laid in double configuration with a block 440mm between each pair. It's well within on there load tables but my main concern now is bounce.

The span if i lay into the existing house wall is 3.5m. There is already an opening which is not being made bigger so it's the additional weight of the floor and a flat roof. My BCO is away til next week as well so I can't run it past her until then and I want to get the beams ordered.

 

[tomfe]

It's well within on there load tables

I was not questioning that, as the beam design is provided by manufacture they would have to be correct otherwise they would be liable if it failed. Whoever designed your extension should have thought about use (bounce) before they sent specified this type of floor.
If you are worried about cutting holes in the original wall you might be able to build a sleeper wall off the original foundations.

 

[noseall]

A couple of dollys and man power. The beams were only 180kg 4 people to push them into place on dollys then the final lift 1 end at a time

Good luck with that.

 

[rssteve]

It's all been designed by me apart from the piling. After all we are on a diy forum. I've done my own drawings and building regs all passed OK. I'm well aware a professional shouldnt of made this mistake but there are posts online about floors being bouncy so it obviously does happen.

I,ve got no issue with cutting into the wall I was just concern about the additional weight making the foundation settle more. Presuming it could after 45 years. The foundation depth is actually nearer to 800mm below gl so hopefully not an issue for me.

Thanks for the useful info.