Concrete lintel sizing

[pertinky]

Hey guys,

I've got a couple of openings I'd like to install in one of the gables of the house for built in wardrobes.

It was originally 2 cottages, and then a subsequent extension was built on the side so we have 4 gable ends (3 double leaf, one normal cavity brick/block construction)

The gable in question is one of the original end gables (double leaf) that adjoins the new extension. Given all the gables its difficult to create space and move rooms around so we're planning on extending two bedrooms that butt this gable by going through and studding the other side to create the alcoves for wardrobes

It massively helps with the layout of the upstairs bedrooms so I feel its some essential work.

Do I need to get an engineer to do calcs for this? The openings are going to be 3ft (so 1200mm lintel)

My plans show the location of one of the openings is where an old window used to be. I can see its been bricked up in the outer skin (inside the new extension the mortar is new), and im assuming I will find the original lintel the other side (going to look today) as I see no reason why you would remove it.

Unfortunately theres no opening in the other location much to my dismay!

The roof construction in the extension has 2 steel purlins that rest on the original end gable that I need to put the openings it if that makes any difference.

 

[^woody^]

65mm concrete lintel will do. Unless there is a purlin or beam directly above within 300-500mm

 

[pertinky]

@^woody^

Would I double up (one for each course in the double leaf)?

By "directly above" do you mean "inside the load triangle"? The two steel purlins would sitting be *roughly* in the middle of the spans but I can measure the distance from the top of the lintel to the purlin. I think it'll be greater than 300, but maybe not 500.

 

[pertinky]

Just had a quick measure as im heading out. A 1700mm opening (height) would leave just over 500mm between top of the lintel, and underside of the purlin

 

[^woody^]

Yeah double it up and that will do. Don't forget the cavity tray.

 

[pertinky]

Thanks @^woody^!

Found the old timber lintel so the top of the opening will be 600mm from the purlin above.

Going to hire a couple of strongboys to hold it up whilst the lintel goes in. Mortar mix above the lintel doesnt look in great shape so better safe than sorry!

Thought cavity tray would only be applicable on external wall? This is an old window opening thats now inside due to side extension

 

[^woody^]

No tray then if an internal wall

 

[pertinky]

Attached a diagram. The red lines are the purlins and the green lines are the proposed openings in the original gable end (double leaf). Joists run from left to right

Just out of curiosity is the purlin supporting the full load of the extension roof, and in turn is it being supported fully by both gables?

I'm thinking two strong boys ought to do it. I believe they will work for double skin too with a small cavity in between.

I've chased out the plasterwork either side today so its ready to go once I'm happy with providing support and correct lintel spec

 

[^woody^]

Sometimes purlins take a lot of load from the rafters, other times just take out the chances of the rafters deflecting a bit.

But normally allow each end of the purlin taking 1/4 the load of the roof.

One prop should be sufficient, with the load spread across several floor joists or you will need a prop in the room below too

 

[pertinky]

Ye I've got floorboards running top to bottom but there are joists adjacent to the wall. I was going to basically put some more timber down running parallel with the floorboards so the weight is spread across 2-3 joists instead of just one closest to the wall/floorboards only