Steel beam size question

[yacobwood]

Hi All,

Im currently building in the garden (digging foundations at the moment) and I have a concern about my lintle. My ridge beam for the apex roof sits in the middle of another beam which spans a double doorway. My concern is that the wooden beam will bend under load and crack the door. So im concidering an i-beam. Any help on replacing the beam over the door with an i-beam would be great

Specs
Base

• Footprint
• 5011mm deep x 4610mm wide
  • Ground screws
  • 1200mm round flange ground screws from thegroundscrewshop.co.uk
  • 100mm L profile fixing bracket
• Beams
  • 145mm x 70mm
  • doubled up around edges
  • 400mm on centres
• Rafters
  • 145mm x 45mm
  • 600mm on centres
  • Simpson SAE250/47 H/Duty Face Fix Hanger 47mm
• DPM
  • 1200 gauge DPM on underside of timber
• Insulation
  • 140mm PIR insulation board (0.022 W/mK)
• OSB
  • 18mm T&G OSB3 (595mm x 2440mm)

Walls

• Beams
  • 145mm x 45mm
  • 3 bolted together, mainly to match the thickness of a stud
• Studs
  • 120mm x 45mm
  • Attached with 3.1mm x 90mm Hot Dipped Galvanised Collated nails
• Top / Bottom pates
  • Single bottom plate
  • Double top plate
• Insulation
  • 120mm PIR insulation board (0.022 W/mK)
• OSB
  • 11mm OSB3 exterior
• Breather membrane
  • Tyvek Housewrap Breather Membrane on top of OSB
• Battens
  • Treated battens 500mm on centres
  • Firstly vertical to create an air gap then horizontal to attach vertical cladding
• Cladding
  • 20mm x 120mm Siberian larch T&G cladding
  • C2 stainless steel 4mm x 45mm cladding screws

Roof

• Beams
  • Two 145mm x 45mm timbers bolted together with coach bolts
• Rafters
  • 145mm x 45mm at 4 degrees
  • 400mm on centres
  • Simpson Strong-Tie RR47 Ridge Rafter
  • Birds mouth joint on wall top plate flush finish
• Outriggers
  • 95mm x 45mm
• Insulation
  • 100mm PIR insulation board (0.022 W/mK)
  • Placed on the lower side of the rafters to create a 50mm air gap above
• Breather membrane
  • Tyvek Housewrap Breather Membrane below the OSB
• OSB
  • 18mm OSB3 exterior
• Roof covering
  • TBC

 

[Spectric]

You should look at the roofing sheets that incorporate the PIR insulation as it makes things easier. I would suggest that your ridge beam in wood would be the better option, that roof shown in your drawing is not going to be heavy as it would be in slate or tiles and the metal beam is just adding weight you don't need. The shallow roof pitch also puts a lot more load on the side walls.

 

[yacobwood]

You should look at the roofing sheets that incorporate the PIR insulation as it makes things easier. I would suggest that your ridge beam in wood would be the better option, that roof shown in your drawing is not going to be heavy as it would be in slate or tiles and the metal beam is just adding weight you don't need. The shallow roof pitch also puts a lot more load on the side walls.

Would you not even change the beam above the door to an ibeam that the ridge sits on?

 

[macca]

judging by the framing you opening is only around 2m, I doubt you'd see much deflection in 3 timbers bolted together, glue them and/or used toothed washers to be belt and braces but i dont think it will be an issue

 

[yacobwood]

Fantastic news. Thanks for putting my mind at ease

 

[Fergie 307]

My concern would be that with such a shallow pitch I'm not convinced your central roof beam will be strong enough to not sag, and lead to the roof flattening over time and the walls splaying. Has anyone done any calculations for you to confirm this will be sufficient?
My very similar workshop, admittedly with a 7m span and 5m long ridge, has an I beam at the apex with 200x50 joists resting on top of it, secured by plates welded to the beam. Not suggesting you need to go to that extreme, but maybe 200x50 for your ridge beams?

 

[Fergie 307]

Also a little confused why you have doubled up the top beams on the walls? Single will be more than up to the job. And the double battening of the walls for your cladding. If you put horizontal battens straight on, over the membrane there is your airgap. Is there any specific reason for wanting to double it? Just seems you are using rather more timber than necessary

 

[TomGW]

I would increase both the ridge beam(s) and the lintel(s) to 200/220mm and notch the ridge beam, not the lintel. It will involve tapering the lintel on both sides but will retain the depth in the centre where it is needed. Contrary to what has been stated, the low pitch will increase the load on the ridge and the gables that support it and reduce the load on the side walls.

 

[yacobwood]

Also a little confused why you have doubled up the top beams on the walls? Single will be more than up to the job. And the double battening of the walls for your cladding. If you put horizontal battens straight on, over the membrane there is your airgap. Is there any specific reason for wanting to double it? Just seems you are using rather more timber than necessary

Having vertical then horizontal battons allows for the air gap from below to flow up into the roof and out the ridge

 

[yacobwood]

I would increase both the ridge beam(s) and the lintel(s) to 200/220mm and notch the ridge beam, not the lintel. It will involve tapering the lintel on both sides but will retain the depth in the centre where it is needed. Contrary to what has been stated, the low pitch will increase the load on the ridge and the gables that support it and reduce the load on the side walls.

Like this?

Need a way now to achieve the clean roof line now like this =/

 

[deema]

I’d throw a couple of hundred at a structural engineer to be sure what is required. That’s a cheap investment considering the cost of materials to build it and what it would cost if it has to be redone.

Just a question, why such a low pitch roof? Equally you can get very low pitch composite roofing tiles that weigh very little and look like say slate that work down to 15 degrees.

 

[Fergie 307]

Having vertical then horizontal battons allows for the air gap from below to flow up into the roof and out the ridge
View attachment 176698

Not really necessary to have a flow as such to ensure proper ventilation of the gap. your cladding will allow air to circulate.

 

[Fergie 307]

I’d throw a couple of hundred at a structural engineer to be sure what is required. That’s a cheap investment considering the cost of materials to build it and what it would cost if it has to be redone.

Just a question, why such a low pitch roof? Equally you can get very low pitch composite roofing tiles that weigh very little and look like say slate that work down to 15 degrees.

For such a shallow pitch you may as well just go for a flat roof, much easier to construct. If you don't like the look you can put a false gable on the end, to get the appearance as your drawing.

 

[yacobwood]

I’d throw a couple of hundred at a structural engineer to be sure what is required. That’s a cheap investment considering the cost of materials to build it and what it would cost if it has to be redone.

Just a question, why such a low pitch roof? Equally you can get very low pitch composite roofing tiles that weigh very little and look like say slate that work down to 15 degrees.

Low litch due to 2.5m height restriction

 

[Spectric]

The low pitch, is that local planing or that you are close to a boundary ? Is there anywhere else to locate it as then you could use a 4 metre height. If you could just move to 2.5 metres from a boundary then a higher apex.

 

[Pedronicus]

Just an observation on the low pitch but if either of the two side elevations face the prevailing winds could there may be an issue during heavy rainfall and strong winds preventing run off and maybe even blowing it back up under the ridge capping?

 

[deema]

I’m not sure how close it is to the boundary which I know makes a difference. I built this back end of last year under permitted development (still needs rendering) roof is at 25 degree pitch.

 

[yacobwood]

I’m not sure how close it is to the boundary which I know makes a difference. I built this back end of last year under permitted development (still needs rendering) roof is at 25 degree pitch.View attachment 176723

So that would be eves hight max 2.5m and ridge max 4m right? so 2.5m away from a border. My garden is only 11m wide and im planning on putting another building side by side so mine is only 40cm away from a boarder. However i love this roof type and dont want to go down the flat roof option

 

[yacobwood]

I would increase both the ridge beam(s) and the lintel(s) to 200/220mm and notch the ridge beam, not the lintel. It will involve tapering the lintel on both sides but will retain the depth in the centre where it is needed. Contrary to what has been stated, the low pitch will increase the load on the ridge and the gables that support it and reduce the load on the side walls.

Like this?

 

[Ozi]

I helped a friend build a very similar sized shed about 4 years ago, as a rough estimate you are using about 10% more timber than he did, the roof was 0.9mm plastic coated rolled steel sheet insulated with recycled plastic insulation (looks like glass fiber but you don't need gloves etc.) very easy and light to install

Roof pitch about the same, it's still standing, still water tight and I can walk on the roof when needed. Sometimes wounder if we could have used less wood but it's seen a couple of goodly storms without issue - think you will be OK.