External wall blocks laid flat

[daunker]

I'm converting a steel portal frame milking parlour, the blocks have been laid flat on one exterior wall for strength. Currently has dropped ceiling and roof sheets off. I want to carry block to full height.

 

Do I need to continue laying them flat or can I switch to conventional. Lower blocks are all 140mm too, but either way was wanting to go to 100mm.

 

There will be cavity and interior block wall. If I can switch or 100mm laid conventionally is there any reason not to up the insulation in the wider cavity, was going to use pir boards

 

[Russell griffiths]

Laying flat is easier. 

Or do you mean you only want a 100mm thick wall. 

[Mr Punter]

If that is the outer leaf of a cavity wall you would not normally extend the joists to it.  Also you may want to get some wall starters or ties fixed to the steels so it ties it all together.

[daunker]

45 minutes ago, Russell griffiths said:

Laying flat is easier. 

Or do you mean you only want a 100mm thick wall. 

Sorry both should have given more details - I don't need the wall to be continued at that thickness - was wondering if I could reduce it to 100mm or even 140mm with just normal blocks laid above the ones laid flat.

 

5 minutes ago, Mr Punter said:

If that is the outer leaf of a cavity wall you would not normally extend the joists to it.  Also you may want to get some wall starters or ties fixed to the steels so it ties it all together.

Ah thanks Mr Punter - it is the outer leaf- but the joists you see there are from it's previous life as milking parlour- it had a dropped OSB ceiling attached to underside of the rafters and a void above - with fibre cement sheets on-top of the angles for the roof. That top row of blocks and joists are coming out. New ceiling will be vaulted to purlin/rafter height, and new metal roof and insulation will be held by the steel frame. On top of the flat blocks I'd ideally like to save time and money by not having to lay them flat, just wanted to know if would be a problem to go step down to 100/140mm thickness? 

[saveasteading]

As Mr Punter says, this needs support. From the steel columns is the obvious, but it may even need more as this looks wide and high. How far between frames and how high will it be?

[daunker]

Steel Frames are 4.5m spacing, and the existing external wall is 2.3m to top of retaining blocks (top layer and rafters to be removed) then 1.8m of new height added to go to roof junction. Roof/ceilings to be supported by steel frame.

 

Will be cavity and then interior block wall (100mm) and this would be tied in to existing external wall. Is this what you were meaning or should the existing walls be tied to the stanchion/to the block on the other side of it.

 

Really just wanted to know if I could put 100mm blocks on top of the laid flat 140mms. But all input very much appreciated.

 

 

[Miek]

You might find some useful information within Approved Document part A. 

 

If you are tying the blockwork to an inner course to create a cavity I would go 100mm standard. No need to block on flat if its tied. 

[saveasteading]

16 hours ago, Miek said:

Approved Document part A

Yes, but in principle fix it to whatever is available, the columns and any roof ties. With the height especially the wall is becoming very slender, but then the cavity wall consruction helps a lot, and especially if you use sturdy cavity ties rather than the wire ones.

Your situation is unlikely to be in any examples, and the flat blocks are likely to be stable in themselves.

Any cross-walls will add a lot of stability too.

[Gus Potter]

@daunker

 

Interesting. But a few questions first.

 

Is it a planning condition that you retain the existing structural frame?

 

That frame from the one photo does not look like it will support a domestic roof load .. 50 year design load as opposed to even an old class one agricultural loading. Can you tell us a little more?

 

Also, the steel frame looks like it will deflect a lot horizontally and if you are relying on it to restrain the walls then the walls will crack if the design is based on this premis. A standard deflection limit of an agriculatural building is column height /100. With blockwork it's height/300 sometimes more.

 

Farmers built these things to just stand up and no more, (they did not mind if the roof dripped a bit - excessive deflection ovals out the fixing holes in the roof cladding so the roof drips a bit in places) to house cattle/ sheep etc not their family.. the main farm house was often of a much more robust construction, houses for workers less so.

 

It may be that your SE has designed this so that the steel frame appears to be intact and doing the work to keep the planners happy, but has actually designed the masonry to stand alone thus you have the solid 9" blockwork. Check with your SE before changing the block specification as going from a solid wall to say a cavity reduces the effective thickness of the wall to resist the loads.

 

It's an interesting topic this.. how you convert agricultural buildings into a house.. made more interesting design wise by the planning constraints in England.

 

 

 

 

[Dudda]

This is a fairly big project. Do you've an architect or engineer on the job who'd have all the info and be able to make a call. Hard to judge steel sizes, centers, wind loads and forces from a photo.

[saveasteading]

2 hours ago, Gus Potter said:

Farmers built these things to just stand up and no more,

Not even that. I was once explaining to a farmer how there is no factor of safety for farm sheds, as there is low risk to people. Also that I was surprised that there weren't lots of collapses in heavy snow or wind. He told me that there were many instances of collapse, covered in Farmers publications.

If you were to combine all the factors of safety it would be about 50%, to keep us safe.

Deflection wont even have been considered.

 

So as Dudda, having had our overview, you should get this checked out.

 

PS...I have seen enough farm foundations to suspect that yours will be shallow and on the rough side.

[Iceverge]

On 14/06/2022 at 11:57, daunker said:

There will be cavity and interior block wall. If I can switch or 100mm laid conventionally is there any reason not to up the insulation in the wider cavity, was going to use pir boards

 

How do you plan to tie the internal leaf to the external?

 

Pir boards are not a great option, mineral wool Batts or Eps beads are better.

[daunker]

On 19/06/2022 at 21:08, Gus Potter said:

@daunker

Is it a planning condition that you retain the existing structural frame?

 

That frame from the one photo does not look like it will support a domestic roof load .. 50 year design load as opposed to even an old class one agricultural loading. Can you tell us a little more?

Yes - class q. SE report said it's fine, the roof is only ply and standing seam zinc, so not pretty light.

 

I'm going to speak to the SE and see you guys have given me plenty to think about - many thanks!

Edited June 21, 2022 by daunker

[saveasteading]

7 hours ago, daunker said:

SE report said it's fine,

That has always intrigued me. How can it have no factor of safety as an agricultural building , but suddenly be ok for domestic use.

 

I asked a respected BCO and he said that this is not overlooked, hence most such need additional foundations. Perhaps yours has additional support.

 

[daunker]

36 minutes ago, saveasteading said:

That has always intrigued me. How can it have no factor of safety as an agricultural building , but suddenly be ok for domestic use.

 

I asked a respected BCO and he said that this is not overlooked, hence most such need additional foundations. Perhaps yours has additional support.

 

Yeah so it's an even 100mm slab throughout and in good condition and at 26 years old it's seen plenty of hoofed traffic. So he has no concerns on it. He's to come back to me on the purlin fixings for roof. But it's only ply and zinc to go on there. I may put some timber purlins for ease of fixing insulation. I think there an acceptance that there is more movement with ag conversions than domestic hence the timber ceilings, but the walls are walls on which note...

 

Spoke to him about the walls and he made very good suggestion, and apologies I maybe sent everyone on a goose chase. But he said cheapest and easiest probably go timber frame ontop the flat blocks. Add less weight and given will be timber clad at that elevation no reason not to really. I don't have any experience with timber, so will ask him to give the spec.

 

Topic has been very helpful to steer me and ask the right questions, and hopefully get a good strategy devised.

Edited June 21, 2022 by daunker

[Gus Potter]

1 hour ago, saveasteading said:

That has always intrigued me. How can it have no factor of safety as an agricultural building , but suddenly be ok for domestic use.

 

I asked a respected BCO and he said that this is not overlooked, hence most such need additional foundations. Perhaps yours has additional support.

 

@saveasteading raises some serious safety issues here. I would love to see how your SE is justifying this. It may be that your milk parlour was over engineered in the first place and you are certain of the steel grade / quality, bolt strength and assessed any corrosion that has taken place over the years.

 

You have an old milk palour probably build before the argicultural codes of design were developed. But to give it the benefit of the doubt lets say that it was designed to an old class 4 agricultural standard. BS502 part 22- 2003. For a class 4 building the design life is 2 years. The latest update of the code has dispensed with the old class 4 as there were too many farm building collapses occuring!

 

Copied below are some extracts from BS 5502 part 22 2003.. this code is now superceeded.

 

To put this into context a house roof designed for the normal 50 year life span (equivalent to class 1) should be able to carry a load of 0.6 kN/msq about 60kg/m sq. Lenders expect that a house structure should have at least a fifty year life span, 60 years is sometimes mentioned by insurers and lenders.

 

The agricutural code class 4 lets you away with half that access load. Part of the reason is that the design life is a lot less, part is to do with deflections and the roof not leaking. They (farmers) did not mind if it bent, swayed a lot under snow and wind load, you will if you are living in it. Also it could invalidate a lot of your cladding / roof covering / window warranties if you exceed the manufactures allowances for movement.. horizontal and vertical deflections.. advise you check their specifications.

 

The other main point is the snow loading. For a class 4 building it is only 22% of the design snow load of a house. Hopefully you can now start to see where the safety issue requires closer examination and why I and others? are curious. Also there are restrictions on how close a low class building can be from a highway, this is to ensure that if it does collapse it reduces the risk to the public.

 

To explain a bit. Pretty much all structures are designed on the basis of probablility of collapse and consequence. A flood prevention scheme for farmers fields may be deisgned on a two year probablility of a flood event occuring (only live stock get killed), a house on 50 years (a few people get killed), a dam above a town / city 200- 500-1000 years (lots of people killed) and so on.

 

Now the access load on a farm building is reduced from 0.6kN/m^2 to 0.3kN/m^2 using the same principle.

 

To summarise and to turn back to @saveasteadinghow do you make / justify that an agricultural building steel frame of a different class and designed (if at all) for lower loading can now suddenly be able to carry the design code loads and life span that are required for a house?  unless the steel was over engineered in the first place, the foundations have been investigated and proven to be of adequate size to carry the extra loads and the steel and base fixings have not been compromised due to corrosion and will not be in over the design life of the house?

 

 

 

Edited June 22, 2022 by Gus Potter

[daunker]

Feels like this is going off on a tangent... 

 

But you both seem genuinely interested. How do I justify the building is sound, well I employed a SE. He came out, inspected and did calculations. I am sure I have already said but the building was constructed 1996 so not ancient. I have cleaned all the steels and zinc phosphated them as you can see in photos. The slab is in good condition. I attach some of the report. Does this answer your question?

[Mr Punter]

Timber frame is good suggestion.  I have seen a lot of bungalow to house conversions done this way.  Standard factory made ones tend to use 140mm x 38mm cls studwork for external walls, with 9mm OSB sheathing and 89mm x 38mm for internal.

[Gus Potter]

On 22/06/2022 at 09:36, daunker said:

But you both seem genuinely interested.

Hi @daunker

 

Yes, it's out of genuine interest and not intended to be any form of criticism. There are few folk floating about on BH that have designed a lot of these structures so was curious how you SE was making it work. I'm particularly interested in the conversion of these types of structure and their nuances.

 

The photo you posted sparked my interest as the frame looked slender, purlins were relatively small looking and I could not see any restraints to the rafters.

 

I see it's a propped frame..central support to the rafter. This relieves the bending force  in the rafter thus you can make it smaller. One consequence of this is that the frame tends to sway more in the wind and these types of frame can be more prone to buckling under certain loading conditions.. they are more sensitive and more likely to misbehave.

 

I would hazard guess that the critical loading case is downwards load plus wind load for this frame and this is reflected in the diagram that shows the deflected shape to some extent. I can quite see the load case used but I assume that at some point the load case of downwards load plus wind has been checked as it's often critical on a frame like this.

 

The bending moment diagram (first diagram) shows the bending forces in the members. You can see that at the bottom of the columns there is a bending force which is a bit less than at the eaves connection. I think your SE has assumed that the columns are fully fixed at the base, this makes a big difference to the analysis and thus you have to be sure that the base connection is really fixed and not just a bit of kid on fixity. Presumably you have investigated some of the column bases and checked their size, the base plates and bolting / encasement? Sometimes you get fixed (Constrado) bases if one of the walls is near a boundary.

 

I may not be relevant but the extract from the report mentions that the existing members are 152 x 76 RSJ's, later in the hand calcs the member sizes are referenced as 152 x 89 UB 16's? I would assume that the sections used in the design checks match up with what you have.

 

Lastly it may well be that your SE is taking into account other factors (maybe connection to the other structure that will remain for the life of the building) that we can't see and thus the frame will be good to go!

 

 

 

 

 

 

[Tosh]

I must say I'm surprised as well. I've converted a steel portal frame commercial to residential and each engineer that looked at it proposed additional steel to stiffen the frame even though that extra steel would be performing almost zero to the load bearing elements e.g. roof, since the new walls would be carrying the new roof rafters. In the end we went with ICF for various reasons so all the columns are embedded with concrete but the issue is deflection of the frame. Even with half the columns in concrete the rafters are moving around fairish. You might be surprised how much that frame moves around - try and borrow a magnetic laser level and clamp it to the steel. Even in a very mild breeze I wouldn't be surprised if that laser line jumps about like a frog on hot coals as the steel sways. Once we finish the next pour and put the glulams between the rafters then this will stiffen the whole frame up but we still had to put a couple of steels in as well to prevent all this deflection in different directions. Also at design stage when we looked at timber frame as well as block construction it was generally accepted if we went down that route that we would need to tie into the steel with special slip ties so that the steel could move under expansion/contraction without causing the blocks/finishes to crack.

Appreciate you've had an engineer look at it but just passing on my experience.

[jen and mark]

Timber frame is definitely the best way to go - built on site is easy and cheaper than buying panels - lots of good videos on You Tube!

[saveasteading]

On 22/06/2022 at 00:22, daunker said:

100mm slab throughout and in good condition and at 26 years old it's seen plenty of hoofed traffic.

No problem with falling through the floor. That slab will have insulation on top of it which is very much weaker.

 

But the foundations are very likely to be very small and shallow. Usually they need enlarging or underpinning, which can be  a huge expense

(If a barn moves and settles into the ground it is still good enough for hay or animals, If a house moves then the tiles crack, the drains stop working and the roof leaks and lots of other things.)

Maybe you have additional columns or supporting walls that you have not mentioned. That can be a good solution.

Ask your SE asap, to explain how this building is being upgraded to the necessary standards.