Which board most enhances the structural stability of a block wall?

[epsilonGreedy]

The motivation behind my question is this:

 

1. During various conversations with different trades on site thay have said the final strength of a house is derived from the combination of its parts i.e. first floor joists stiffen the block inner walls and so do the roof trusses, even the dot & dab plasterboard adds rigidity to a wall apparently.
2. I have expended many brain cycles thinking about the support of my false hipped roof chimneys built up from wall plate height. Three experts including my build control inspector have reassured me that a corbeled brick plinth is fine to support the 250mm internal overhang of my 1215mm x 550mm chimneys.

 

Anyhow to tip the balance of structural stability in my favour when an 80 mph gust strikes my false chimney, I have been thinking that a strong plasterboard could add a few extra percent of stiffening to the internal block wall supporting the chimney.

 

Which extra strong plasterboard would most help in this situation?

 

Firmacell: https://www.fermacell.co.uk/en/dry-lining

Habito: https://www.british-gypsum.com/products/gyproc-habito?tab0=0

Glasroc: https://www.british-gypsum.com/products/glasroc-f-multiboard?tab0=0

Cement Particle board: https://www.vivalda.co.uk/products/building-boards/cement-particle-boards/#:~:text=Cement bonded particle boards are,ceilings%2C general lining and acoustics.

 

p.s. The false chimney will be built from full sized facing bricks, so it is only false in the sense it does not have a flue and the corbelling starts at nose height in the bedroom below.

 

 

[PeterW]

None of the above ..???

 

Steel up the middle would do it if it’s false but I’d want it a fair way down the cavity. 

[joe90]

Old fashion chimney brace

 

 

[epsilonGreedy]

16 minutes ago, joe90 said:

Old fashion chimney brace

 

 

Thanks I was not aware of such a device, my chimney will be a similar size though having a hipped roof means less support from surrounding roof carpentry in my case.

 

Some chimneys on the older properties in the village could benefit from such a brace. One reason my chimney is 2.5 bricks wide is that when I mentioned to the architectural technician that the local heritage style is 2 bricks wide he quipped "how many of them have a lean?". 

[joe90]

A big old house near where I lived in Bristol had these which is where I got the idea ?.

[epsilonGreedy]

15 minutes ago, joe90 said:

A big old house near where I lived in Bristol had these which is where I got the idea ?.

 

 

My house is meant to look as though Jane Austen might have visited 220 years ago, a chimney brace could help reinforce that impression.

[epsilonGreedy]

1 hour ago, PeterW said:

None of the above ..???

 

Steel up the middle would do it if it’s false but I’d want it a fair way down the cavity. 

 

 

Fair point, I should have asked a simpler question.

 

"Which board is the strongest when subjected to a variety of loads e.g. compression, tension and bending?".

 

I suspect it will be the Glasroc or particle cement board. The hardiebacker cement board UI purchased earlier this year in 6mm and 12mm thickness is incredibly strong stuff.

[PeterW]

Yes but it’s only as strong as the fixings - how do you plan to attach it to the bricks ..?

[Declan52]

Can you not hide a steel beam/ concrete lintel in the joists of the first floor and start the false chimney from this point.

[Gus Potter]

2 hours ago, joe90 said:

Old fashion chimney brace

 

 

Thanks Joe90. Simple, elegant? and proven to work..but how? Seems to me it mostly works in tension to stop the chimney falling towards the side of the roof we can see as we look at the photo rather than the other way? Anyone here know why?

[epsilonGreedy]

1 hour ago, PeterW said:

Yes but it’s only as strong as the fixings - how do you plan to attach it to the bricks ..?

 

A double portion of dot and dab cement or something more adhesive.

 

The concept is to stiffen the internal block cavity wall 2m below the corbled chimney support and say 1.5m either side so a total reinforced wall panel 6m2 in total.

[epsilonGreedy]

56 minutes ago, Declan52 said:

Can you not hide a steel beam/ concrete lintel in the joists of the first floor and start the false chimney from this point.

 

In hindsight I should have built a complete internal chimney breast off a subwall in the fonds.

 

Many new builds in my village have a false brick chimney sitting on a metal gallows bracket welded insitu into the gable cavity wall. Given my hipped roof the solution recommended by multiple experts was a brick plinth at wall plate height with the corbel starting 8 bricks below wall plate. The centre of gravity of the chimney is within the 300mm wide cavity wall so the corbelled plinth will only experience significant strain during high winds.

[joe90]

9 hours ago, Gus Potter said:

Thanks Joe90. Simple, elegant? and proven to work..but how? Seems to me it mostly works in tension to stop the chimney falling towards the side of the roof we can see as we look at the photo rather than the other way? Anyone here know why?

it simply stops any movement of the brickwork by being braced against a triangulated roof structure.

[Ian]

@epsilonGreedy

Have you considered a pre-fabricated GRP chimney? You can't tell they're not real brick from ground level and it would completely get rid of the structural worry that you have.

https://www.capvond.com/grpglassfibre_mockchimneys/mockchimneys.php#:~:text=Many types of GRP mock,smooth through to roughly texture.

 

and there's also GRP ones which are designed to take a real brick slip facing in case you need it to match:

https://ibstockbrick.co.uk/wp-content/uploads/2016/08/Ibstock-Kevington-Chimney-Brochure-July16.pdf

Edited July 7, 2020 by Ian

[MJNewton]

We've got a brick slip faced GRP chimneystack and had no idea for 9 years since moving in.... I always knew it was 'fake', insofar that we don't have a chimney or flue within the house (2007 'new build'), but it was only when fitting an MVHR unit in the loft did I begin to wonder exactly how the stack was supported and then discovered the existence of these things. Even now I know it's fake I still can't tell from looking at it.

[Gus Potter]

Yes Joe90 is bang on. But to dig a bit deeper and this leads into solar panels.

Lots of chimney braces are say 1 a half inches wide x say 1/4 to / 3/8 inch thick in old money so the they work in mostly tension if they are long. In other words  they act like a bit of rope. Good for tension “pulling on the rope” but have you tried standing  on the end of a bit of rope? Thus putting it into compression? Never mind, Joe90 is pretty close I think so no need to split hairs.

One reason I picked up on this is that I ask.. is it  akin to  when you stick something on a roof like a solar panel? Is a solar panel subject to wind load? Will the wind either push the panel into the roof or more importantly suck the panel off the roof. Or damage the panel it’s self? Do we just trust the manufacturer of the panel that it will all be all right on a windy night?

Yes, the supporting brackets for solar panels are designed to  carry the weight of the panel and any snow that falls on it but does anyone know how you deal effectively with the wind loads on solar panels etc.

Question for the experts? How much can a panel bend before it stops working?

If you live in Scotland say at a higher altitude and in the UK generally the wind can be pretty severe to say the least. So can the wind loads not outweigh the snow loads from time to time? If you live in Scotland/ Wales and parts of England the snow loads can be pretty severe but so is the wind. Can anyone give advice on buying solar panels for windy places too?  Input on this would be much appreciated.

 Any advice from the solar experts or anyone really would be much appreciated. Every day is a school day!

[joe90]

33 minutes ago, Gus Potter said:

Lots of chimney braces are say 1 a half inches wide x say 1/4 to / 3/8 inch thick in old money so the they work in mostly tension if they are long. In other words  they act like a bit of rope. Good for tension “pulling on the rope” but have you tried standing  on the end of a bit of rope? Thus putting it into compression?

I disagree, a steel bar 1 1/2” x 1/4 -3/8” is not like a bit of rope, yes it may give a little under extreme compression but a lot more than wind load on a chimney that would probably survive even without a brace.

 

with regards solar panels they must be “fit for purpose” so the wind load calcs must have been done, different if you just did a DIY job.

Edited July 8, 2020 by joe90

[Gus Potter]

Hi Joe.

In reverse order.

To quote you “with regards solar panels they must be “fit for purpose” so the wind load calcs must have been done, different if you just did a DIY job.”

I think you have touched on a good point. I agree with you in terms of the “fit for purpose”, not so sure that a DIY person should settle for something less though.

Now the “fit for purpose” you mention. I raised this as I’m not so sure about how the manufacturers of solar panels are approaching wind loading. Yes, they may be designing their panels to take the odd heavy fall of snow, say two or three feet every 20/ 50 years, but what if you live in a rural area where  the wind will bend them significantly every few months in the winter say?

Over to the experts?

I have been wondering if the manufacture’s address this more frequent bending of solar panels under wind loading, I struggle to see them doing this as the wind loading varies significantly depending on where you place the panels on the roof. Forgive my naivety but it seems to me that if you keep bending a solar panel it will break sooner than you think?

Hopefully some of the roof / solar experts will chip in with their advice and clear the air on wind loading regarding Joe’s reasonable statement that they should be “fit for purpose”.

Joe’s chimney brace!

I appreciated your  photo and description of what a chimney brace looks like. You explained that well and succinctly, the old skills, knowledge and experience seem to be neglected at times, your comment is refreshing and straight to the point. Thank you for that. The technical side is for another day.

Thanks again Joe.

[dpmiller]

Certainly in terms of fixings etc the likes of GSE are very definite about the number of nouting points and batten sizes etc to stop even their flush mounting system being sucked off the roof.  There's detail in the MIs

[Carrerahill]

On 08/07/2020 at 23:13, joe90 said:

I disagree, a steel bar 1 1/2” x 1/4 -3/8” is not like a bit of rope, yes it may give a little under extreme compression but a lot more than wind load on a chimney that would probably survive even without a brace.

 

with regards solar panels they must be “fit for purpose” so the wind load calcs must have been done, different if you just did a DIY job.

I'd suggest getting a 6' piece of 1 1/2 x 1/4 steel bar, place one end against something solid and give it a good push at the other, report back.

 

 

[epsilonGreedy]

On 07/07/2020 at 08:14, Ian said:

@epsilonGreedy

Have you considered a pre-fabricated GRP chimney? You can't tell they're not real brick from ground level...

 

 

I have a fancy buff brick blend prescribed for my new build which is in the centre of a conservation area village, this is unlikely to match any GRP brick finishes.

 

On 07/07/2020 at 08:14, Ian said:

and there's also GRP ones which are designed to take a real brick slip facing in case you need it to match:

https://ibstockbrick.co.uk/wp-content/uploads/2016/08/Ibstock-Kevington-Chimney-Brochure-July16.pdf

 

When I started my build I assumed the non working chimney would be a non masonry stick on false chimney stack. Recently I got a quote for an unclad false 1.8m tall chimney which was not far short of £2k. Even when clad with only 20mm slips this would have been too heavy to manually lift into place which meant asking my brickie to clad it insitu with some very expensive glue. This cladding process would have required 45 degree bevel cuts on the outer corners.

 

Mounting one of these is not trivial particularly given the free standing height. My understanding is that the weight of a full brick chimney provides the lateral stability to resist window force hence in the absence of much weight in a false chimney some chunky fixing mechanism is needed.

 

After thinking through this option for a week I decided to go for a full brick chimney sitting on a corbel. When my brickie, building control inspector and retired builder advisor all said a corbel plinth would be up to the job, it was simpler to follow their collective wisdom.

 

I think a grp chimney would make sense when the chimney is short and mounted within a gable end and conventional ridge.

[Gone West]

12 hours ago, epsilonGreedy said:

This cladding process would have required 45 degree bevel cuts on the outer corners.

Why wouldn't pistols be used instead of bevel cuts.