Installing an RSJ - Looking for Advice on how to install

12 Apr 2013
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United Kingdom
My house is a 2007 build and i'm planning on removing the 3m wall between the kitchen and dining room to open it up. The wall is a breeze block support wall, supporting the upstairs floor joists only.

Plan of action
Get RSJ calculations from a structural engineer
Notify Building Control and pay fee
Hire 6x acro props and 2x scaffold board (use 3 acro's both sides of the wall supporting ceiling via scaffold board)
Remove wall
Install 2 padstones, 1 either end of the RSJ support wall with 150mm+ of room for RSJ to sit on
Measure and order RSJ and install, concrete in to place
Plan visit for building control to inspect
Make good, using fire resistant plasterboard

Does that sound like i'm doing it right? Anything obvious i should be aware of or missing?

1. Can the padstones sit on the existing breezeblock walls from the adjacent walls at either end of the RSJ or do i need stronger supports for the padstone blocks? (one wall that the RSJ will sit on is the external wall so may be brick?) Just not sure if breezeblock is strong enough for padstone supports

2. If i want to move the RSJ into the ceiling void so its hidden, can i cut the floor joists and install the RSJ in the void then use RSJ hangers attached the RSJ to hang the joists?
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The order of work seems OK.

Instead of putting a forest of props up, consider just 2, or max. 3, strongboys.

The 'breeze block' walls (actually aerated concrete block) will be fine for the padstones; the SE will design the size of the padstones required,
which depends on the strength of the block, and the load being carried.

You can push the beam up into the thickness of the floor by cutting joists and using joist hangers, but it is fiddly work.
2. You would bolt timbers into the RSJ and hang your joists of them.

Do you have a Structural Engineer? If your after a recommendation then I used one recently and was very happy with the service I received.
1 Yes.

2 You need timber bolted in the web.

You should have the beam ready before you start. Sometimes it's easier to put the beam in before all the wall is removed. You don't need a 150 bearing and you should not need any nibs either.

And it's often easier to put the padstones in after, if the beam is below the joists, as you need to jack the beam up tight first. If the beam is going in the ceiling, then you might not get it in with padstones in first.

You might need additional props to push the beam up
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Great, thanks for the advice!

I take it 3 strongboys wouldnt work in my case if i plan to insert into the void as will need support both sides of the wall once the joists are cut?

Putting the padstones in after the RSJ has been put in place sounds wise and yes will need props for the RSJ too thanks

I dont have a SE, if you can recommend one that would be appreciated.
I did also see a couple of websites offering RSJ calculations for £50, should i run a mile or they fine to use?

Finally can i use any timber to fit along the RSJ for the hangers or does it have to meet a certain regulation, and is it simply a matter of drilling 2-3 holes through the steel and bolting the timbers together either side and then nailing the hangers to the timber? I presume there is a maximum hole size i can drill so i dont degrade the strength of the steel?
I used the steel beam calculator first but then had to get an SE because my council (Rochdale) don't accept the online ones. They want the authors name and qualification on them.
thanks for letting me know Ian - do you know what i should expect to pay for an SE for this job, £300-£400?
Bit less I would expect. I'll send you his e-mail now.
Be worth asking BC about steel size, when I did my kitchen / diner knock through my BC guy advised what to install and signed it off once fitted. If a SE calc is needed, about £80 approx per calc if its simple.

I put my pad stones in first but you must let the mortar go off for a few days before plonking the steel on top.

Top tip, depending on the room layout look at putting your steel against the wall before you put the props up so you can just lift it straight up and in.

If you need to fireboard it then be wise to fix timber to it for fixing to, you dont want to be bashing in fixing timbers once the steel is in. Space accordingly to board wise.
thanks for letting me know Ian - do you know what i should expect to pay for an SE for this job, £300-£400?

If you are under Birmingham building control, then they will accept certain sized beams in standard loading situations without engineers calculations.

For that span a 178x102x19kg/m UB may well do (depending on the floor spans), if not a 203 X 102 X 23kg/m UB certainly will - but will that fit in the floor void?
really appreciate the advice and tips!

I'll call my local BC officer tomorrow to see what they say

Many thanks
I notified BC and paid their fee a couple of weeks ago, they need calculations for the RSJ however it doesnt need to be from a SE - they just need calculations which they informed me could be from the RSJ supplier so based on that i could use the online form but will see if they RSJ suppliers can provide this

I opened up the area over the weekend and there a 6 water pipes in the area which are going to be too much work to reroute so i've decided not to recess the RSJ which should make it an easier job overall

However i'm unsure on the padstone supports:


1. The wall by the window i presume i can cut out one of the breezeblocks and replace with a padstone?


2. If so do i need to put a strongboy support in this wall as its supporting the breezeblocks above when i cut out the breezeblock?

3. The adjoining hallway wall on the left is very thin aerated concrete (guessing 4inches thick), i presume this wont be suitable to support the padstone? If not will i need to leave approx 6 inches of wall on the left for the padstone to support the RSJ?
If only supporting a floor, the loads won't be that great so you would not normally need to leave a nib.
Hello Ian, I am building a rear single storey extension and might need to put a rsj in the middle to cut the timber roof span in half, could you give me the contacts of your SE as you said Rochdale doesnt accept online one. Im in Rochdale area as well. Cheers.
Get 8 Acrows and a pair of stout planks.

Get some slate (Marley eternit are perfect) packers.

Prop the ceiling each side of the wall using a plank and three Acrows each side. Position the plank about 600mm away from the wall each side.

Plan how you are going to thread the beam in or have it on the correct side of the props ready.

Smash the wall down but make sure you highlight where any cable or pipe runs are prior to using a breaker.

Remove enough material for the padstones and the beam on the two bearing point walls.

Remove the masonry at and below floor level allowing enough room for screed.

Insert the beam onto the masonry. Manually jack up the beam each end using wood or brick chocs. When the beam is almost touching the joists insert an Acrow at one end and jack it up snug. The plasterboard ceiling should be enough to prevent sway but be careful once the weight is on the Acrow. Do the same at the other end but make sure you have another man attending the other Acrow so that it doesn't come free.

Jack the Acrows tight to take up the joists. You may need to use slim packers under some of the joists if there is a wee bit of difference in seating. This may also require you to remove some of the ceiling plasterboard to do so.

Mortar bed the padstones beneath the beam. Use the packer material to fill the remaining few millimeters.

Remove the six props and planks but leave the two under the beam until the mortar has set.

Make sure your beam has pre drilled holes in the web so that you can bolt in a timber sandwich each side. We use coach screws through one beam (and the web) into the other.

Double board the beam and make good floor and walls. Don't forget DPM for the floor.

If you hang your side plasterboards down say an extra 25mm below the beam bottom, you can then fix a piece of 4" x 1" beneath the beam by screwing through the side plasterboards into the 4" x 1". This will give you something to fix the underside plasterboards to. Use 30mm screws for the first (bottom) layer of plasterboard.
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