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I want to move a purlin prop which rests on bathroom wall to make room bigger


Buildabear
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Hi all I’m new to the site, my first task is to make the bathroom bigger. I want advice with this. As you can see in the photos what the issue is the wall I want to take down Is supporting the purlin via a 3x3 timber. Can I just build a frame on a plate out of 4x2 across the whole of the way across the joists or is there a better way of doing this? 
 

thanks in advance 

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F25E5A0D-C0F6-46A1-B02C-38693F915303.jpeg

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Not easy to answer specifically as we don’t know what, span etc of the joists.

what is the section and span of the purlin?

might be easier to turn the purlin into a trussed member to enable it to span without support.

If you definitely want to remove the whole wall you could add a steel and the prop sit on top of that in the loft space (steel to bridge wall to wall)

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1 hour ago, Buildabear said:

The joists are 400 c and they span just over 3 m wall to wall

Couple of noggins between joists either side of the wall and then a diagonal from the end of the wall to the purlin. You are not looking at big spans or loads (steep pitch roof), possibly an additional vertical as you say spread over a couple of joists to be doubly sure

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9 hours ago, Buildabear said:

Hi all I’m new to the site, my first task is to make the bathroom bigger. I want advice with this. As you can see in the photos what the issue is the wall I want to take down Is supporting the purlin via a 3x3 timber. Can I just build a frame on a plate out of 4x2 across the whole of the way across the joists or is there a better way of doing this? 
 

thanks in advance 

BCF2577E-654A-4BD3-9AC9-581D86AD954D.jpeg

F25E5A0D-C0F6-46A1-B02C-38693F915303.jpeg

Welcome Buildabear.

 

Well done you for taking this on. I hope you find the following info helpful and that it will give you some pointers as to what you may want to consider.

 

Firstly and again well done..you have identifed that the 3x 3 post is splitting the span of the purlin. If the purlin is continuous between the masonry walls it will be attracting a bit more load than you would expect. Story for another day but the post will often be carrying more than 50% of the roof load if the purlin is continuous.

 

Your starting point here is to have a look at the wall you are taking away and what it is doing. Is it just carrying some vertical load or is it also providing sideways (lateral stability to another wall? Often walls perform both functions.

 

In the top photo you can see that the wall has been toothed / bonded into the external wall pretty well and to the right hand side there is a window. I'm guessing but is there a window to the left we can't see? If so when you take the wall away you'll be left with a bit of masonry between the two windows which now becomes a column that has significantly reduced lateral support between the floors and ceiling. Often you find that the column can cut the mustard when subject to a bit of wind load.

 

Now lots of folk will say.. don't be so dramatic..! as we have done the same or seen other houses that have had this kind of alteration say 30-40 years ago and they have not fallen down. But back then you maybe had good solid timber windows or metal framed windows. This framing often added enough strength to maintain the stability and strength of the wall. But over time these were stripped out and replaced with plastic windows and pretty rubbish brackets so the old rules no longer apply. For the curious there is a bit in the BS design codes that touch on this swapping solid framed windows for more flexible frames.

 

It would be worth having a chat with an SE to see if the things I highlight are relevant before you commit to much or take down more of the wall. It may be that all is fine but if you can get some confirmation from say an SE it could ease the way not least when you come to sell in case a surveyor takes the same analysis (ask questions) approach as I have outlined above. Do this and it may allow you to progress with confidence in the knowledge that you are definitly improving the value of your home with much less risk?

 

All the best with the project and keep us posted on your progress. Oh, and don't forget to put up a photo of the finished article.

 

 

 

 

 

 

 

 

 

 

 

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It is also possible that the purlin is half-lap jointed where the purlin strut is? If so brace that when undertaking any alterations ;) 

 

A pair of 9x2's sistered together running from the remainder of the wall to the internal leaf of the exterior wall should more than suffice and is a one day job. Jack the purlin up with an Acrow until you just see the strut wanting to lift. Cut it and lower back down onto the new timbers and secure with some construction screws. Do not use regular screws for any of this work ;) 

Edited by Nickfromwales
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20 hours ago, Buildabear said:

is there a better way of doing this?

As you'll at least be moving water connections, the job will fall under Building Regs anyway. First question form BC you'll get will be about structural engineer's assessment for demolition of the wall.

We can give you plenty of ideas, but if the roof collapses (or any other shit happens) it will be all on you: no insurer will pay a penny because 'buildhub folks told me so'

Get an SE

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3 hours ago, Nickfromwales said:

It is also possible that the purlin is half-lap jointed where the purlin strut is? If so brace that when undertaking any alterations ;) 

 

A pair of 9x2's sistered together running from the remainder of the wall to the internal leaf of the exterior wall should more than suffice and is a one day job. Jack the purlin up with an Acrow until you just see the strut wanting to lift. Cut it and lower back down onto the new timbers and secure with some construction screws. Do not use regular screws for any of this work ;) 

Thanks nick, the loft has 3 purlins, 1 on each of the external walls, semi detached. It’s not half lapped from what I can see.
 

I’m sorry I’m not very technical, I did a 2 year carpentry course with my employer as a secondary apprenticeship but as you could imagine it’s not very thorough and through lockdown didn’t get to college much and didn’t end up passing. 

 

so you mean use the 9x2s straddle the opening like a lintel?

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