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Category: Structural Engineering
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We have had a conservatory built, but part of it does not look

Customer Question

We have had a conservatory built, but part of it does not look right. It is a traditional lean-to type with glass roof supported by a wall plate at one end and eaves beam the other end with a long (about 3.1m) triangular window fitted above the PVCu framed side windows. There is no physical fixing between the triangular window frame and the outer roof support beams, just a plastic trim stick on the inside/outside. There is a gap running from the house wall to the outer eaves beam, about 40mm at the wall end narrowing to nothing at the eaves beam, this is what the plastic strip covers. The plastic strip prevents the eaves beam end covers and wall plate end covers from fitting properly but that is the only real exterior indication that something is not right, the lack of fixings and gap I observed and questioned during construction but the answer did not convince. The side walls/windows do not seem to be very sturdy and can easily be flexed with a fairly gentle tug/push. Some photos can be viewed here:!112&authkey=!ACBqb_pSNvF4cDk&ithint=folder%2cjpg
My question is, does this look/sound right, or should I be concerned?
Thanks in advance for any assistance.
Submitted: 1 year ago.
Category: Structural Engineering
Expert:  StructuralEng replied 1 year ago.
I can help. Can I get back to you in a few hours?
Customer: replied 1 year ago.
Yes, no problem. Let me know if you have any problems accessing the photos through the link, I could then try to upload the images using this medium's "add files" function.
Customer: replied 1 year ago.
Photos added. The "end cap" photos only show part of the symptom but do indicate that a plastic strip has been added solely to cover the gap (that I think should not be there) and is preventing the end caps from fitting properly.
To clarify my question in three parts:
1) Has the conservatory been erected properly, with reference to the further questions below
2) Should there be fixings between the outer "starter" beams to the UPVC window frame below
3) Are the roof support beams correctly interfacing with the wall support bracket (is bad interface causing the excessive gap)
Customer: replied 1 year ago.
(Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  StructuralEng replied 1 year ago.
I think that gap should be there to allow the mullion above to deflect vertically without loading the glass directly below it.
Customer: replied 1 year ago.
The reason for asking questions was to try and determine whether we have a problem, or not. And, to either alleviate our concerns or give confidence to challenge the installation.
I assume that when you sate “mullion”, you actually mean the outer horizontal beams stretching from wall plate to eaves beam, right? (
I’m afraid that your short response just raises more questions and increases concern:
- Why would a metal reinforced beam “deflect”
o This beam (and the others) support much larger glass roof panels, surely “deflecting” would put stress on those panels
o This beam is fastened to the wall plate and the eaves beam at either end, by “deflecting” would it not put stress on these connections? and…
o … stress the much larger glass panels connected and below the eaves beam?
o If the beam deflects vertically, then is it not likely to also flex horizontally, potentially imparting twisting stress on all of the above?
- If the beam were securely fastened to the side walls, surely it would help prevent any deflections?
o The triangular (indeed all) windows, within their frame, are supported by “soft” cushions and held in place by rubber (or similar material) surrounds and not rigidly fixed to the frames. Would this not allow a fairly high degree of isolation from deflections anyway?
- If the gap and lack of fixings from roof support bean to side wall is needed, then does this not indicate a design flaw that gives inadequate support for the side walls/windows?
As stated previously and shown in the various photos, the poorly fitting end plates and trims, either demonstrates poor workmanship, maybe including errors in erection, or is the result of a design flaw that the fitters are trying to cover-up.
In either case, I am still seeking confirmation either way. I would much rather have minor problems with “finishing” as opposed to a design or erection problem. I hope you can convince me that the latter is at least unlikely.
Expert:  StructuralEng replied 1 year ago.
All beams deflect, no matter how big they are or how little they support. It's a physical impossibility for a beam to not deflect. The idea is to manage the magnitude of deflection and to accommodate the movement in pieces that can't tolerate it. The glass on the roof is being supported by the mullions, not loaded by them. If the mullion deflects, but is resisted by the vertical glass, then the vertical glass is supporting the mullion. That is a scenario that you don't want.
Customer: replied 1 year ago.
I would have more confidence in your statements if you used the correct terminology. "Mullion: a slender vertical member that forms a division between units of a window, door, or screen or is used decoratively". Look at any dictionary you choose to confirm this definition.
That aside, I have found a number of installation instructions for lean-to conservatories, unfortunately for other brands of conservatory, that specifically state the outermost support beams (their terms: glazing bar and starter beam) should be screw-fixed to the window frame every 500mm, I have attached two examples and these apply to raked frames with no mullions (using the above definition) through to using five mullions. I have also attached examples of raked frames aligned with the same instructions.
While I have no doubt that you are correct in that "all beams deflect", I have my doubts that it applies in this case with a relatively short (less than 3.5m) metal "I-beam" due to the other points I mentioned, but you seem to have ignored.
I feel we are going nowhere here as you have failed so far to convince me that a gap is "correct" and you are focusing on just one element of the information I have provided... Unless you have something more relevant and detailed to contribute, maybe you should consider opting out of this question and allowing another expert to contribute.
Expert:  StructuralEng replied 1 year ago.
I design structures for a living. I know the definitions of which I speak. I am not concerned with the dictionary definition of a mullion. I know what a mullion is. I will opt out for you. Good luck with your project.
Customer: replied 1 year ago.
OK, thank you.
Expert:  Shantal-Mod replied 1 year ago.
I’m a moderator for this topic. It seems the professional has left this conversation. This
happens occasionally, and it's usually because the professional thinks that someone else might be a better match for your question. I've been working hard to find a new professional to assist you right away, but sometimes finding the right professional can take a little longer than expected.
I wonder whether you're OK with continuing to wait for an answer. If you are, please let me know and I will continue my search. If not, feel free to let me know and I will cancel this question for you.
Thank you,
Customer: replied 1 year ago.
Thanks for your message, can we wait a few days. I may have an answer from another source but it's always nice to have additional confirmation.
Expert:  Shantal-Mod replied 1 year ago.
No problem, thats fine. I will keep your question open and see whether theres a Professional who can assist you.
Thank you,
Customer: replied 1 year ago.
Well, I got my answer from the conservatory manufacturer and later confirmed by the "new" fitters that came to correct the problem. There should be no gap, there is no need to allow for "deflection" and the roof and sides are designed to support each other but (obviously) this can only happen if they are all securely connected together. So, my suspicions were confirmed and the installation was done badly, but is now "fixed". So much for the "expert" that doesn't believe in dictionary definitions!
Customer: replied 1 year ago.
Can you now please close this question and refund my card.
Thank you.