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    • CommentAuthormarsaday
    • CommentTimeDec 17th 2017
     
    Do you think i need to use a steel bearer plate for my oak lintel over the patio door ?

    All i need over the 3m opening is a 250 H x 150 W mm oak beam. So my reclaimed brick outer skin will be taking the full load of the flat roof above.

    However, i feel using a 300 x 300mm section of oak will be better because half the beam will sit on the more structural block internal wall and concrete padstone. Plus i get a more chunky looking piece of oak and so i am going down this route.

    Do you think i will still need a bearing plate say 3mm thick sitting over the brick outer skin ?

    Or would you have a bearing plate the full wall size, so spanning to sit on the inner block wall as well. Someone has mentioned this will now be a thermal bridge and so cause some problems.

    The beam weight is likely to be 300kg as it is partially air dried for a few years. If it was green it would be approx 380kg in weight.
  1.  
    Who specified the steel bearer plate? Who specified the beam? Are they equally happy with a beam nearly 2.5 times the weight, even though it will be carried on both skins of the cavity wall?

    As regards the thermal bridge, yes, a lump of steel in half the depth of the wall is less of a bridge than in the full depth, but can you not get away without it, if you increase the bearing length?
  2.  
    If you want a steel bearer plate why not have 2, one on the outer skin and one on the inner skin, that way there is no thermal bridge between the inner and outer skins (assuming the cavity wall is a typical approx 300mm that will match the 300x300 beam)
    • CommentAuthormarsaday
    • CommentTimeDec 17th 2017
     
    The engineer specified a lintel for the patio door opening = 250 x 150mm.

    So much smaller than what i am thinking of using. But this lintel would be fully weighted on the external brick wall wouldn't it. Should he have mentioned the bearing detail for this ?

    No one has specified the steel plate, this is something i have been thinking about. So if i used a smaller beam resting on the external brick only i wonder if the brick would be a suitable padstone?

    I suppose i need to ask him if this sized oak will be ok above my patio door and if i can go bigger.

    The 250 x 150 beam at 3.5m in size will weight about 100kg (set on brick external wall)

    The 300 x 300 beam at 3.5m = 300kg. (set on brick and block walls)
    •  
      CommentAuthordjh
    • CommentTimeDec 17th 2017
     
    Posted By: marsadayThe engineer specified a lintel for the patio door opening = 250 x 150mm.

    So much smaller than what i am thinking of using. But this lintel would be fully weighted on the external brick wall wouldn't it. Should he have mentioned the bearing detail for this ?

    I presume he was talking about an oak timber as the lintel? Either he should specify the bearing detail or he should provide a reference to an established detail that he assumed.

    No one has specified the steel plate, this is something i have been thinking about.

    It sounds like you are inventing problems for yourself. Ask the engineer what detail to use and then decide whether you have any issues with what he has actually proposed.

    Why do you want to introduce a thermal bridge ( the 'chunkier' piece of oak)? You'd probably do well to give the engineer a better description of what you want and ask him to specify it.
    • CommentAuthormarsaday
    • CommentTimeDec 17th 2017
     
    What happens when you build a timber frame house then ? All the oak is a thermal bridge surely?

    The oak above the patio door is to be exposed inside. It will be not clad behind insulation and plaster board.

    So it will be a thermal bridge whether i use a thinner piece resting on the external brickwork or a chunkier piece resting on the inner and outer walls.
    • CommentAuthormarsaday
    • CommentTimeDec 17th 2017
     
    <blockquote><cite>Posted By: Peter_in_Hungary</cite>If you want a steel bearer plate why not have 2, one on the outer skin and one on the inner skin, that way there is no thermal bridge between the inner and outer skins (assuming the cavity wall is a typical approx 300mm that will match the 300x300 beam)</blockquote>

    Yes this is probably the best solution. But internally i will use a concrete padstone. It is over the brickwork where i think i need some extra strength.

    I am also using a bearing of 250mm approx rather than the standard 150mm. So there is more area to bear on.
    •  
      CommentAuthordjh
    • CommentTimeDec 18th 2017
     
    Posted By: marsadayWhat happens when you build a timber frame house then ? All the oak is a thermal bridge surely?

    No, the oak frame is either inside the house or outside it, not both. That's on a modern insulated house, of course, not a 16th century cottage.
    • CommentAuthorCWatters
    • CommentTimeDec 18th 2017 edited
     
    Can I check.. The proposal is to use a steel lintel on the outer leaf and an exposed oak beam on the inner leaf?

    Has the SE proposed a type/design for the lintel? Is there a cavity tray?

    The SE should specify if any pad stones or bearing plates are required and their sizes.
    • CommentAuthormarsaday
    • CommentTimeDec 18th 2017
     
    No i am using an oak purlin only above the patio door.

    The SE said a 200 x 150 oak lintel for 4m was needed.

    My opening is now down to 3m and i want a bigger piece of timber over the door.

    He never specified any detail for the bearings.

    So the original oak will weight about 100kg. Thats 50kg on each end.

    I want to use a 300kg approx beam on both cavities. So 75kg on each leaf, 150kg at each side.
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