Double Door Lintel on Load Bearing Wall Advice

[SmokeyC]

Hi

I have a 762mm Internal Doorway downstairs.
I want to install Double Doors to a Kitchen/Diner (1981x1372x44), and just looking for advice.

Upstairs Wall
The Wall I think is Concrete Block, though I am not sure if its hollowed out. It is 133mm with the render so I think its fairly standard 100mm thick + render
Above the downstairs wall is a same construction upstairs wall.
This big internal wall runs parallel to the roof tie beams - so I don't believe it takes any roof load.

Floor
The wall has noggins above which support the parallel running joists.
There is a I-Beam at 90deg attached to the wall further down the same room (the beam supports the parallel joists and a wall above supporting a cut truss roof).



Do I need a structural calculation for this or can I put in a hollow box or concrete lintel?

I've been looking at the interactive zone and load triangle and reading posts on here; its probably just caused a little confusion..
If I were to buy say a 1800mm steel reinforced concrete lintel, would that really support the load of the upstairs wall?

Are the calculations a necessity?
If not, for peace of mind I have seen high strength lintels supporting 3x the load of a 1800mm Wicks pre-stressed concrete lintel.

Any advice would be greatly appreciated?

 

[George_engineer]

A few hundred pounds on a structural engineer is probably a good idea.

Alterations to load bearing walls is a Building Regulations matter so you'll need to get them to agree to the plan. Would avoid any issues when you came to sell the property.

For what it is worth, I recently did a design for a similar opening in an internal wall and on site I thought a normal lintel would do. When I ran the numbers, it did require a high-strength lintel. It is not just the strength, it is also the size, bearing and checking the remaining wall itself (although for an internal wall it is rarely an issue. A structural engineer would also check the other load paths (roof, wind forces, foundations etc) that internal walls can sometimes non-obviously play a role in.

 

[^woody^]

Put two 65mm concrete lintels in (one bedded on top of the other) or a standatd steel box lintel in.

I would not [waste] money on an engineer for what is a standard loading situation.

 

[George_engineer]

Perhaps it doesn't need an engineer but I have to point out that bedding a lintel on top of another one does not improve the strength. That is, two 65x100 is not the same as a 130x100 because you are relying on mortar to transfer the shear stresses and any amount of cracking removes any additional strength. All it would do is allow for a bit of extra load distribution through the top lintel.

 

[jks7492]

Yes a standard concrete lintel will be fine - something like a Naylor R6 will do.

 

[jks7492]

A few hundred pounds on a structural engineer is probably a good idea.

A few hundred pounds on a structural engineer is definitely a waste of money.

 

[George_engineer]

A few hundred pounds on a structural engineer is definitely a waste of money.

It will depend what the building control inspector says.

I think in the context of a house worth £100ks it is not unreasonable to get a professional opinion for a tiny fraction of that price. While I absolutely accept that most internal walls won't need anything special, if the roof is loading the internal wall in an unusual way or the floor spans are especially large, then a bog standard lintel isn't always enough.

 

[jks7492]

It will depend what the building control inspector says.

For an opening that size the building inspector will probably tell you what lintel to use!

 

[tony1851]

A few hundred pounds on a structural engineer is probably a good idea.

Particularly for the structural engineer.

 

[George_engineer]

For an opening that size the building inspector will probably tell you what lintel to use!

I'd hope so. Old school ones definitely would. Not sure Approved Inspectors would want to.

 

[George_engineer]

Particularly for the structural engineer.

Some people don't mind gambling with houses (usually not their own), others over-design and others ask an engineer.

I can charge a lot more for fixing the gamblers problems than the ones who ask first. The over-designers earn me nothing.

 

[^woody^]

but I have to point out that bedding a lintel on top of another one does not improve the strength. ...... All it would do is allow for a bit of extra load distribution through the top lintel.

Isn't "extra load distribution" effectively "more strength" in this context?

The only issue is the load distribution.

But I am pretty sure that a house built out of concrete lintels would keep the little pig safer than his pen pal in a house of brick

 

[tony1851]

@ George: as a matter of interest, what would be a 'reasonable' quote for the following;

3m opening, central in 4m-long 102 brick wall between front and rear reception rooms in 1930s semi;
floor runs parallel to wall on both sides:
supports similar wall above, supporting only bedroom ceiling joists running 3m perpendicular (no purlin props etc).
??

 

[George_engineer]

@ George: as a matter of interest, what would be a 'reasonable' quote for the following;

3m opening, central in 4m-long 102 brick wall between front and rear reception rooms in 1930s semi;
floor runs parallel to wall on both sides:
supports similar wall above, supporting only bedroom ceiling joists running 3m perpendicular (no purlin props etc).
??

Calculations for building control and a drawing, between £150 to £250. Probably more in London.

You can get those sorts of calculations done online for about £75 - but you don't get a site visit and I doubt their professional indemnity would cover anything.

I like to think that I'd can sometimes justify my fee aside from legal compliance - if a builder/building control just want to put in an 8" beam but I show that a 6" is actually fine, then I'd paid for most of that cost already. Not always possible of course.

Isn't "extra load distribution" effectively "more strength" in this context?

The only issue is the load distribution.

But I am pretty sure that a house built out of concrete lintels would keep the little pig safer than his pen pal in a house of brick

Technically no, but I know what you mean. Bricks are nearly as good at spreading load via arching action so it's not a big improvement. If the lower lintel did fail, having another one the same size on top isn't going to help. Last thought.... two 65x100 lintels is basically the same price as a stronger 140x100 so I don't see why you wouldn't just get a 140.

 

[Dereekoo]

Perhaps it doesn't need an engineer but I have to point out that bedding a lintel on top of another one does not improve the strength. That is, two 65x100 is not the same as a 130x100 because you are relying on mortar to transfer the shear stresses and any amount of cracking removes any additional strength. All it would do is allow for a bit of extra load distribution through the top lintel.

Interesting conclusion, if I had a lintel that was taking a load y then the deflection would be 10mm( say) if I halved the load the deflection would be 5mm. I then take the load away and place a similar lintel underneath the original one and reapply the load y. The top lintel deflects as does the bottom one in equal measure. When the top lintel has deflected 5mm it will be resisting a load of y/2, similarly the bottom one will be resisting a load of y/2 hence the total load resisted will be y. Taking this through to a deflection of 10mm then each lintel will be resisting a force of y giving a total resisting force of 2y. The lintel weights are ignored for this simplification. To me it is the same as put a scaffolding plank on top of another which makes things less bouncy which reflects the decrease in loading per board. Obviously a single lintel of twice the depth increases the available resisting force more than 2 laid together. Thoughts?