RSJ on thermal block

Discussion in 'Builders' Talk' started by 132blackrs, Jan 13, 2020.

  1. 132blackrs

    132blackrs New Member

    IMG_0522.jpg Hi all. I'm after some advice please. A family member is planning on widening an existing opening between his lounge and dining room. At the moment it's about 1.8 metres wide (double door width) but he wants to remove the load bearing wall and go right back to the outside wall on the one side. The clear opening will be around 3 metres. He's had some advice and was told that he can set the RSJ onto the internal cavity wall (thermal block) using some engineering brick under the beam to add some load bearing. I'm no expert but I thought this might not be right. The RSJ will then support 10 first floor joists and the bedrooms above (no solid walls just stud above). I thought you need a minimum of 150mm bearings for the steel and I do believe the thermals will be 100mm wide. I was guessing he would be better off cutting the existing single block load bearing wall back and keep six inches to bear the steel. The other side of the beam will sit on a decent amount of the existing solid block wall so that's ok. Any advice from you pro's is greatly appreciated.
  2. stevie22

    stevie22 Screwfix Select

    Whoever specs the beam will spec the padstones. We aim for 150mm but in such cases as yours 100 onto the padstone which is set at right angles to the beam is fine,

    If side wall is long you may need to keep a bit of pier to buttress the wall. Again your SE will advise.
    Jord86 likes this.
  3. 132blackrs

    132blackrs New Member

    Ok thanks stevie. The other bit I hadn't mentioned is that he was also advised that he could do what he liked in his own house and wouldn't need to have it signed off by local building control. This doesn't seam right either from what I've read. TBH I'm just checking to make sure he isn't doing anything wrong or potentially dangerous. If he goes ahead then I don't think an SE will even see it. He is very careful and thorough but it might be he's been wrongly advised so just wanted a second opinion.
  4. carl24bpool

    carl24bpool Active Member

    When removing load bearing walls the work is subject to building regulaitons. However it is not notifiable or subject to planning (unless its a listed building) and therefore you don't have to tell your local authority about the work and you don't need a building inspector to sign it off. Any involvment of a BI would be for advice and guidance but I would be getting this from a structural engineer as they will be needed either way to specify the size of steel to install.

    I would just use some 150 or 225mm concrete lintel cut to the length of a block as pad stones with 100mm on to each. Rock solid and a bit cheaper than a purpose made padstone.

    The wall is holding very little in terms of load, so as long as your steel is the right size then you should be fine with the rest.
  5. 132blackrs

    132blackrs New Member

    Thanks for the reply Carl. Yes not much weight above just preventing the joists sagging I suppose. He's ordered the beam (7" deep by 4" wide) so he'll just need to make sure it's bedding right then. Thinking about it now the load is taken by the whole of the thermal block to distribute the weight even though the beam is only resting across 4 inches.
    Last edited: Jan 13, 2020
  6. Jitender

    Jitender Screwfix Select

    I don't think they are thermal blocks.

    Look more like concrete blocks from here.
    ginger tuffs likes this.
  7. ginger tuffs

    ginger tuffs Screwfix Select

    t he catnic is sitting on a course of bricks as jitender said they are they are concrete blocks
  8. Jitender

    Jitender Screwfix Select

    Yes the work will be subject to Building Control.

    The builder may be using the correct sized beam. I think BC will costs about £120 (last years prices).

    They may not want any SE calculations as they deal with this on day to day basis, if they want calculations it could costs another £250.

    May seem a bit excessive but if you need to sell house in future then it may not be covered.

    The current lintel is about (6") 150mm height, so putting in a 7" (178mm) rsj will entail more work. ie working to brick courses. Could have went upto the next size 203mm and may have been better with taking and cutting half bricks etc.

    Or alternatively go for a extra heavy duty catnic box lintel, which are 219mm in height, which work to block sizes, all depends on SE.

    If the plan is to make one room rather than reinstating the opening, would be better to place the lintel further up the wall?
    Last edited: Jan 13, 2020
  9. Jord86

    Jord86 Screwfix Select

    The external walls are, they plan on removing the entire dividing concrete block wall and rest the RSJ on the thermalite inside skin of blockwork.
  10. carl24bpool

    carl24bpool Active Member

    Its rare to use thermal blocks on internal walls due to it being quite pointless and costly.
  11. Jitender

    Jitender Screwfix Select

    Think I must of read that wrong. But he dose say one wall.

    Definitely get BC involved though.
  12. carl24bpool

    carl24bpool Active Member

    For what reason?
  13. Jitender

    Jitender Screwfix Select

    Especially with the load on the thermalite blocks, may need to use padstones on the side that's going into the wall.

    The pillar that will be left will be strong enough though ( may need a smaller sized paddstone)
  14. carl24bpool

    carl24bpool Active Member

    All this can be done by the structural engineer that he will need for steel calcs anyway.
  15. stevie22

    stevie22 Screwfix Select

    OP: contrary to what some above have said the work DOES need a sign off by building control or an approved private inspector.

    Your relative will have trouble selling without paperwork.
    Abrickie likes this.
  16. Severntrent

    Severntrent Screwfix Select

    Because when he comes to sell it he will have to lie through his teeth that he hasn't done any structural changes to his house or admit that he has and either provide BC sign off or indemnity insurance for the work carried out
  17. 132blackrs

    132blackrs New Member

    Thanks for all your advice on this. Yes the internal wall is thermal block on this house and the new beam will of course be installed up to and touching the joists. I think he's going to call the BCO this week to speak to them and check just to be sure.

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