Roof truss lintel support

[John Smith Esq.]

Hello,

Just interested to hear any thoughts on this. The roof truss company "helpfully" designed a roof where the main girder truss goes over a doorway and sits on the wall plate of the internal wall, below which is a timber lintel. This didn't become apparent until we started putting the roof up. I asked them if this is definitely ok structurally and they replied something like "we only do above wall plate, check with your engineer". Like I have one of those on hand. They did say it should be fine.

Anyway, builder suggested as a precaution putting a lintel under it on the outer skin as well so well supported and we got a nice thick wider one, which goes past doorway 300mm either side. He has used little steel plates as packers between the top of the outer skin and the bottom of the truss. One thing I notice is that this means the weight is concentrated on some small plates on a single concrete common on top of the lintel.

Thoughts on this general arrangement? Still time to make adjustments.

 

[noseall]

they replied something like "we only do above wall plate, check with your engineer"

Were you expecting the Roof Truss company to design your extension?

Like I have one of those on hand

Like most folk consult one prior to engaging in a structural project.

. They did say it should be fine.

?

Anyway, builder suggested as a precaution putting a lintel under it on the outer skin as well so well supported and we got a nice thick wider one, which goes past doorway 300mm either side. He has used little steel plates as packers between the top of the outer skin and the bottom of the truss. One thing I notice is that this means the weight is concentrated on some small plates on a single concrete common on top of the lintel.

Thoughts on this general arrangement? Still time to make adjustments.

It looks ok to me.

Ordinarily, a single PCC jobby would unlikely be man enough without composite coursing of masonry above it. As you have used a 140mm deep fella, I'd say you should be ok. Building Control, may need to check it or have your own SE approve it.

One thing I notice is that this means the weight is concentrated on some small plates on a single concrete common on top of the lintel.

Ideally, the lintel would have been better lower. i.e. just above the door head.

 

[John Smith Esq.]

No I was not expecting them to design my extension. That was done by the technician who prepared the plans and who called for a trussed roof structure. He didn't design the roof; he, along with several builders I spoke to, said the roofing company would design it and they would follow instructions to install it. I was told that if I wanted an old type, cut roof then an engineer would need to be engaged. Not so for the trussed one. Perhaps they were wrong then.

The roof truss company had a copy of my plans and surveyed the site, so I would expect them to have considered the doorway and flagged if it was a concern or likely required input from an engineer, bearing in mind this would cost me half what the roof itself has. The plans they provided before I accepted the quote didn't even show the door and it was only as we were installing it that we realised the main girder truss sits above the doorway. I wonder if he forgot.

Anyway, it is what it is, more fool us for not realising that the roof company isn't bothered at all about what is below or the implications for the customer. We will know for in future. I don't think it is true that most people do consult an engineer before constructing a single storey extension - they might have their plans prepared by an architect or building technician as I have. I have asked the roof company if this idea of an additional lintel is ok and he said it is overboard I'm his opinion but he isn't an engineer when it comes to below the wall plate.

Thank you for your other comments.

Should I get an engineer in then to check for peace of mind? The idea is for the truss to be on the inner and outer skin but now it is 1mm above the inner skin since the builder raised the truss slightly to get the metal plates in on top or the new outer skin lintel. So he is going to see if he can get something under the gap to the inner skin. Tiles haven't gone on yet so time to get it right before the real weight goes on there.

 

[noseall]

No I was not expecting them to design my extension. That was done by the technician who prepared the plans and who called for a trussed roof structure. He didn't design the roof; he, along with several builders I spoke to, said the roofing company would design it and they would follow instructions to install it. I was told that if I wanted an old type, cut roof then an engineer would need to be engaged. Not so for the trussed one. Perhaps they were wrong then.

The roof truss company had a copy of my plans and surveyed the site, so I would expect them to have considered the doorway and flagged if it was a concern or likely required input from an engineer, bearing in mind this would cost me half what the roof itself has. The plans they provided before I accepted the quote didn't even show the door and it was only as we were installing it that we realised the main girder truss sits above the doorway. I wonder if he forgot.

Anyway, it is what it is, more fool us for not realising that the roof company isn't bothered at all about what is below or the implications for the customer. We will know for in future. I don't think it is true that most people do consult an engineer before constructing a single storey extension - they might have their plans prepared by an architect or building technician as I have. I have asked the roof company if this idea of an additional lintel is ok and he said it is overboard I'm his opinion but he isn't an engineer when it comes to below the wall plate.

Thank you for your other comments.

Should I get an engineer in then to check for peace of mind? The idea is for the truss to be on the inner and outer skin but now it is 1mm above the inner skin since the builder raised the truss slightly to get the metal plates in on top or the new outer skin lintel. So he is going to see if he can get something under the gap to the inner skin. Tiles haven't gone on yet so time to get it right before the real weight goes on there.

Did your designer not check this before approving his design? Most experienced designers are aware of truss roof layouts and their quirks. The roof truss company isn't to know whether you intend putting a steel over the opening or just bricking it up. If the surveyor was made aware, they can jiggle their design.

 

[John Smith Esq.]

The roof designer did know there is a door. The same one on site is shown on the plan of my extension which they used to design the roof.

What sort of engineer do i need to engage to have a look at this and advise if it is safe or not? Likely cost?

 

[noseall]

The roof designer did know there is a door. The same one on site is shown on the plan of my extension which they used to design the roof.

What sort of engineer do i need to engage to have a look at this and advise if it is safe or not? Likely cost?

I'd see what BC say first. Ordinarily we'd be putting something like a wee bit of 152 x 89mm steel UB across. They (BC) may be happy with a 140mm fella along with a course of bricks.

 

[John Smith Esq.]

BC will probably want to see an engineer's report. If I do need such an opinion what kind of person am I looking for, preferably not too expensive and willing to just have a look and do quick letter or email?

 

[noseall]

BC will probably want to see an engineer's report. If I do need such an opinion what kind of person am I looking for, preferably not too expensive and willing to just have a look and do quick letter or email?

A local Structural Engineer could prove that lintel for a few hundred £££ (if it is man enough) with their eyes closed. Photos inside and out probably all that is needed.

 

[John Smith Esq.]

Righto, thanks!