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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorKenny_M
    • CommentTimeJul 18th 2019
     
    Hi all,
    Hoping some of you involved in building might be able to comment on this. As part of plans to upgrade our extension from the minimal/non existent insulation levels of its original 1990 construction we are replacing the failed PVC windows and doors with triple glazed Russell Timbertech (tip from Tom some time back). My wife would very much like to also convert the windows and door in the pic to two large doors, one replacing the large window on the left with a door and the window door combination on the right with a single door.

    My first thought after looking at the proposal was that to cut out on either side of that pillar would probably leave too small a section of wall to support the lintels supporting that entire section of roof. The original builder that my wife got out quoted but didn't mention anything about this. The joiner that I got out right away said the same thing that I was thinking and said he wouldn't touch it and he said it would probably need a steel support, and also seemed to think that the existing wooden lintels would need to be replaced with steel.

    https://www.dropbox.com/s/3jo11t0qiew2kqu/Extension%20photo.jpg?dl=0

    Not sure how to approach this, if it needs an architect or structural engineer, or what the likely cost of all of this would likely be. Any thoughts welcome.

    Thanks
    Kenny
    •  
      CommentAuthordjh
    • CommentTimeJul 18th 2019
     
    If the existing lintels are wood and the openings are not going to be widened then I don't see why the existing lintels would not be sufficient. Unless you're planning on top-hung bifolds or something?

    I think you might need a steel support post in the corner, yes, but something like a scaffold pole would likely be sufficient. I suggest opening up the corner to see what is there at the moment. Again whatever it is the loads aren't going to change so what's already there should be sufficient.

    FWIW, our sun room has longer runs of windows & doors so we had to use some steel in the lintels, in the form of flitch beams. Our corner post is just a wooden post though. From memory, the post is 100x100 and the beams are made up of 2 no 45x150 timber sandwiching a 10x150x(3000 or 4000) steel plate. The roof is flat, EPDM over ply, and there is a lightweight rooflight in the centre. All the glazing is triple-glazed, PHI level. I don't remember the cost of the flitch plates but it wasn't much from a local metalworking shop. Their design was a small part of my structural engineer's work but again it wouldn't have cost much.
      sun-room-flitch-beams.JPG
    •  
      CommentAuthordjh
    • CommentTimeJul 18th 2019
     
    Here's a detail view of the corner.
      sun-room-corner-detail.JPG
    • CommentAuthortony
    • CommentTimeJul 19th 2019
     
    I reckon yours has an big l shaped lintel with a steel corner post, probably massive thermal bridges everywhere.

    The roof does not look very heavy

    Simplest is remove window and look and see

    The corner post will be near impossible to insulate, think in terms of adding hundreds on millimetres of insulation to it.

    Some wooden windows could easily carry the roof load but finding someone to sign that off will be impossible now.
  1.  
    Posted By: tonyI reckon yours has an big l shaped lintel with a steel corner post, probably massive thermal bridges everywhere.

    If it is a steel corner post it would probably be possible to replace it with the correct grade timber which would reduce the cold bridge a lot. You will have to do some invasive investigation to see what you have.

    I would agree with the comments above in that a lintel over a window will be good enough to be over a door, if you are not going to widen the hole, however the possible problem with your plan is that if you take the wall under the window out (for the doors) whilst this is usually OK, in your case the structure of the corner might be compromised as it is so close. If that is the case it might be easier to take out the whole corner putting in a new corner post ground to roof then you could do the lot in (properly insulated) timber frame.
    •  
      CommentAuthordjh
    • CommentTimeJul 19th 2019
     
    There's only one way to determine what the existing construction is and that's to strip back enough of the coverings until it's possible to see what the structural materials really are. You might be able to decide what exactly the lintels and corner post are just by drilling deep holes into them from the inside and seeing what you hit.

    Then again, you might need to take off more, especially around the corner. But it's all just cosmetic damage and will be ripped out anyway when you do the real building work.
    • CommentAuthorCWatters
    • CommentTimeJul 19th 2019
     
    Since 2002 anyone replacing windows should check the work complies with all aspects of the Building Regs eg including Part A (Structure) and eventually notify the LABC of the work done. My understanding is that a member of Fensa (or other competent person scheme member) should be able to check this for you. However I have my doubts that they are all suitably experienced to do so.

    If you use a general builder (who isn't a competent person scheme member) you/he will need to make a Building Control Application or Building Control Notification for which there is a fee. You can't rely on the Building Control Officer telling you what needs to be done but many will give informal advice if you keep in their good books.
    • CommentAuthorKenny_M
    • CommentTimeJul 19th 2019
     
    Thanks all, this is very helpful. I cut a piece of the outer hardboard trim away this afternoon, and then had to very swiftly patch it up as the rain came down heavy.

    From what I can see the supporting corner post is definitely wood. It appears to be resting directly on the top of the concrete sill that you can see in the picture. The concrete sill looks like it continues across the cavity wall. I can’t see any metal bracket holding the post in place. It’s actually a little rotten at the bottom, which is not surprising as when we moved in the hardboard trim was rotted away at the bottom before I temp patched it up with filler and repainted.

    https://www.dropbox.com/s/sa2w2mphp2jfwjp/2019-07-19%2014.21.16.jpg?dl=0

    So, it seems that it would be possible to remove the windows, brace the existing lintels then knock out the wall and the existing corner post, then replace with another wooden corner post as required and secured at floor level to the concrete foundation with a metal bracket?

    Not sure that I have the experience or time to do this myself, although probably the thing I would be most nervous about is the bracing. Anyone got a ball park idea how much this should cost to do (excluding the cost of the doors)? The builder my wife got out was quoting ÂŁ6.5k+ vat for the job, including the straight replacement of two other windows on the extension, but excluding the doors/windows cost.
    • CommentAuthorKenny_M
    • CommentTimeJul 19th 2019
     
    Thanks CWatters. I have already started a building control application, (also needed planning approval as in a conservation area).

    Building control have asked a number of questions, as I expected, and most are easy things for me to answer, but one relates to the lintels and support. I was waiting until I was a bit more informed before I call to discuss, and I was hoping to have a builder onboard by the time I got to this stage to help answer.
    • CommentAuthorKenny_M
    • CommentTimeAug 3rd 2019
     
    I am considering doing this job myself as I can't seem to find a decent tradesperson who wants to take it on because it's not a standard swap out. Would appreciate those with more experience - which is probably everyone :) - sanity checking this plan for me.

    I took off the external trim yesterday to see how it was put together. Pic - https://www.dropbox.com/s/4e2kzzcrswyl3z6/2019-08-02%2019.21.46.jpg?dl=0 The post appears to be one 150x50mm piece on the right, nailed to three 100x50mm pieces on the left, to make one 150mm² post. Resting on top of this are 200x50mm lintels going in each direction, and my impression is that these are doubled up, i.e. there is another 200x50mm piece behind each of these. The main joists for the roof are resting on top of the one going off the the left. Not sure how the post and lintels are connected, but I presume that they are just nailed together. The woodwork that I can see all looks in good condition, except for some rot where the post sat on the dwarf wall, but this is because the outer plywood trim had been allowed to rot by the previous owner and had left the post exposed at the bottom.

    As this is all done in wood, and a makeshift 150mm² softwood post has been holding it up for about 30 years, I figure that a single 150mm² structural oak post would be at least as effective, and would match up to the timber above. Something like this - https://www.uk-timber.co.uk/air-dried-oak-beams/63-air-dried-oak-beams-150mm-x-150mm.html

    When the wall is taken away I'll probably have to level it off with concrete. Not sure whether it would be best to dig down and concrete the post in below floor level (would this rot?), or level off in line with the concrete floor and then use something like a post shoe to retain it at the bottom?

    There is enough overhang from the roof to put a decent amount of insulation around the two exposed faces of the post, and on the outside of the timber lintels, then protect with painted plywood trim to match what is there just now. The timber windows should presumably screw into the timber lintel and post, and the block/brick at the other side.

    This will need to be approved by building control who I am hoping to meet next week, who might in turn ask me to get a structural engineer to verify the loading, but does this seem like a reasonable approach?
    •  
      CommentAuthordjh
    • CommentTimeAug 3rd 2019
     
    Sounds like a reasonable plan to me.

    Not sure how the post and lintels are connected, but I presume that they are just nailed together.

    Could well be. It might be sensible to plan to use nail plates to connect them in your refurbishment. That's what my SE specified anyway.

    As this is all done in wood, and a makeshift 150mm² softwood post has been holding it up for about 30 years, I figure that a single 150mm² structural oak post would be at least as effective, and would match up to the timber above.

    Using multiple smaller timbers nailed together is a poor man's version of laminating timbers. It means there are no weak spots running all the way through the timber at any point, so whether they're better or worse than a single post I don't know. I don't know how oak beams are structurally graded, but make sure you get one that is suitably rated.

    Not sure whether it would be best to dig down and concrete the post in below floor level (would this rot?), or level off in line with the concrete floor and then use something like a post shoe to retain it at the bottom?

    I'd be worried about rot if you bury the end, so I'd use a shoe or some brackets every time.

    The timber windows should presumably screw into the timber lintel and post, and the block/brick at the other side.

    Think about how you're going to fix the screws and where the screw holes will be and how you'll make good the heads. If you screw straight through the frame you'll end up with visible holes on the inside of the frame. That's one reason you might use metal brackets to fix the windows so the screw heads are on the outside of the frame and buried in the wall. But you need to look at the particular situation and window design that you have.
    • CommentAuthorKenny_M
    • CommentTimeAug 4th 2019
     
    Thanks djh, that's brilliant, much appreciated.


    Posted By: djhCould well be. It might be sensible to plan to use nail plates to connect them in your refurbishment. That's what my SE specified anyway.

    Thanks, good tip.


    Posted By: djh I don't know how oak beams are structurally graded, but make sure you get one that is suitably rated.

    Yes, I will need to learn a bit more about that. The oak 150mm² post beam I saw said it was suitable for structural use, but had no other information or spec. The structural engineer that I emailed said on his site that he specialised in timber, although I think he might be more large scale so I may not even get a response.


    Posted By: djhUsing multiple smaller timbers nailed together is a poor man's version of laminating timbers. It means there are no weak spots running all the way through the timber at any point, so whether they're better or worse than a single post I don't know.

    Funny, I was thinking when I was looking at it that there might be some structural benefit from multiple timbers. Also something to look into - it would certainly be easier to get, and cut to size, structurally graded timber in smaller sizes. Found a site - https://www.structuraltimber.co.uk/library/ - that seems to have a lot of info.
    • CommentAuthorKenny_M
    • CommentTimeAug 9th 2019
     
    Close to completing my 2nd draft of drawings, and hopefully gaining building standards approval. Just thinking about the post, and when I cut the wall to floor level and extend the timber corner post, it will be straddling an open cavity wall at floor level, instead of the concrete sill that it currently rests on.

    To get a level, solid base I was thinking I could pour some concrete into what remains of the cavity and skim it level on top of the runt wall.

    Alternatively I could fit a treated timber sole plate, over a damp course, along the top of the wall, anchor the sole plate to the wall, and the post to the sole plate.

    Any thoughts or advice welcome as always.

    P.S. The floor level is raised above outside ground level and this will all be insulated and boxed out, so dampness on the post shouldn't be a concern.
    • CommentAuthortony
    • CommentTimeAug 10th 2019
     
    No wooden plate for me,
    • CommentAuthorKenny_M
    • CommentTimeAug 10th 2019
     
    Why not Tony?

    I had been thinking that I need a wooden plate to raise the doors anyway, and had thought I might just run that all the way around the floor, with the post resting on top. I had been looking a timber framed house recipe book I found on the web, from the New Zealand building standards site, and that seems to be what they do - i.e run a sole plate all the way around the concrete floor and tie the frame into this. Only difference here is that this is a wall, rather than a slab.
    • CommentAuthortony
    • CommentTimeAug 10th 2019
     
    It will go rotten if it gets wet and will decay over time, A dpc will stop damp from below bur will not stop it getting wet from condensation on top of the dpc. Water has a habit of getting in.
    •  
      CommentAuthordjh
    • CommentTimeAug 11th 2019
     
    I would put polystyrene under the doors rather than timber. A bit more insulation and less likely to rot. Doors are supported by the sides of the frame, so the only load on the sill is people walking across it etc.

    You may be fine with timber under the post, but if it's possible to use concrete instead then that removes one more risk as Tony says.
    • CommentAuthorKenny_M
    • CommentTimeAug 11th 2019
     
    Thanks Tony and djh.

    I was thinking about insulation under the doors instead of wood, but thought it wouldn't take the load. That would be brilliant if I could use it under the doors, and would help with conduction around the perimeter. Is EPS ok for this or would it need to be XPS, which I think has a higher compressive strength?

    Is there any potential issue with filling what remains of the cavity with concrete to give a sold base?

    If not I could possible reuse a piece of the concrete cill, cut to the width of the post and the depth of the wall, cement in place across the wall to take the base of the post and act as a spacer. Then pour some concrete into the cavity underneath, which would also allow me to sink metal brackets into the concrete in the cavity to fix to the base of the post.

    I intend insulating the post from the outside, to below where it terminates, which should help with condensation.

    Sound ok?
  2.  
    Compacfoam is rigid high-density EPS which we have used for cills. Solid as a rock but more expensive than standard EPS or XPS. On the other had it was a small (ish) piece and we knew it would never move.
    • CommentAuthortony
    • CommentTimeAug 11th 2019
     
    How about foamglass
    • CommentAuthorKenny_M
    • CommentTimeAug 11th 2019
     
    Thanks guys, a few good options for under the door. That sounds much better than timber.

    Anyone able to comment on whether its ok to pour concrete into the cavity?

    I guess there might not be a cavity at all at that level, but if there is it would be a good way to secure the bottom of the post with a bracket set in the cement. Only issue I can think of would be the concrete putting pressure on the walls, but it would be a relatively small amount.
    • CommentAuthortony
    • CommentTimeAug 11th 2019
     
    Adding to the thermal bridge, I cantilever the screed over the cavity filling it with eps. Difficult or wide ones like mine get paving slab with pir on the edge where they touch thresholds.
    • CommentAuthorKenny_M
    • CommentTimeAug 12th 2019
     
    Posted By: tonyAdding to the thermal bridge, I cantilever the screed over the cavity filling it with eps. Difficult or wide ones like mine get paving slab with pir on the edge where they touch thresholds.


    There should already be EPS in there, from the cavity wall insulation.

    I suppose my greatest concern with this job is stability and load bearing, rather than the thermal properties, because it will be fairly easy to insulate from the outside right down to below where the post will terminate

    As it is a single post taking the weight of most of a 12m2 roof I just want to ensure that it is done right. I suppose that a slab laid across the cavity is all that the current cill is, and I could just reuse this.

    Just as a thought, would a thermalite block be suitable for this application? Compressive Strength of 7.3 N/mm² is I think higher than some building bricks, though not sure about it spanning the cavity.
    • CommentAuthortony
    • CommentTimeAug 12th 2019
     
    yes
    • CommentAuthorKenny_M
    • CommentTimeAug 12th 2019
     
    Thanks Tony.
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