Wall piers

[TANK]

Hey guys

I'm wanting to install wall piers on my outbuilding as the length is 6m. Asked about this in my original thread but had no response. I wouldn't ask without first doing my own research, but I can't seem to find a definitive answer (maybe 'coz there isn't one!) either by Google or with the likes of you tube.

My footings lie around 750mm below where the screed flooring will be. Do the piers always rise with the rest of the wall at the footings, or can they start from the screed (which will be 50mm on top of 50mm insulation atop hardcore.)? The first 5 courses are eng brick which then gives way to thermalite. 

 

Im hoping it's the latter as I have overlooked them and will need to do a little remedial work if I'm to go back to the footings... 

 

Thank you

[Declan52]

They really should be started on the concrete foundations. 

50mm of screed is not a lot to rest a wall on. What type of screed are you using, sand cement or a flow type screed??

 

[markc]

50mm screed on top of insulation will break up very quickly. Screed is not like concrete and even then 50mm on top of insulation is pretty week as a floor. Pillars on top of this are more likely to cause problems with the wall rather than support it.

[TANK]

Thanks declan. That was my concern too, although it won't be holding much weight (only single skin thermalite to ~1.90m), it may still be asking for trouble. 

I haven't decided upon type of screed yet. Still a novice with all this although I was leaning towards liquid. 

[TANK]

Good point Mark. You are both right of course. Suppose I Was hoping for a quick fix /short cut to the problem, but it pays to get it right first time. 

Do the piers need to be of a certain size, and of matching material, or could I use, say, a small pier of brick all the way up? It's just that the footings aren't hugely wide and might struggle to accommodate a large pier. 

 

EDIT 

I probably should've included the dimensions : it's 6m x 2.75m x 2.5 high. 

Edited July 21, 2021 by TANK

[Mr Punter]

This sounds like it is outside building regs so maybe don't bother.  Unless you are in a really exposed location the roof will help hold it together.  Use restraint straps on the rafters.

[Gus Potter]

6 hours ago, TANK said:

Hey guys

I'm wanting to install wall piers on my outbuilding as the length is 6m. Asked about this in my original thread but had no response. I wouldn't ask without first doing my own research, but I can't seem to find a definitive answer (maybe 'coz there isn't one!) either by Google or with the likes of you tube.

My footings lie around 750mm below where the screed flooring will be. Do the piers always rise with the rest of the wall at the footings, or can they start from the screed (which will be 50mm on top of 50mm insulation atop hardcore.)? The first 5 courses are eng brick which then gives way to thermalite. 

 

Im hoping it's the latter as I have overlooked them and will need to do a little remedial work if I'm to go back to the footings... 

 

Thank you

Hello TANK.

 

A few thoughts, some explanation which may give you some pointers and another few for all who may be considering knocking down a wall say between their kitchen and dining room in a modern house to form an open plan space.

 

"I'm wanting to install wall piers on my outbuilding as the length is 6m. Asked about this in my original thread but had no response. I wouldn't ask without first doing my own research, but I can't seem to find a definitive answer (maybe 'coz there isn't one!) either by Google or with the likes of you tube.

 

You probably won't as there is a fair bit to it..

 

"My footings lie around 750mm below where the screed flooring will be. Do the piers always rise with the rest of the wall at the footings, or can they start from the screed (which will be 50mm on top of 50mm insulation atop hardcore.)? The first 5 courses are eng brick which then gives way to thermalite."

 

Normally they rise from the footings.

 

"Im hoping it's the latter as I have overlooked them and will need to do a little remedial work if I'm to go back to the footings... "

 

Yes in the spirit of BH there is always hope and mostly a solution..only available on BH of course.. this can take a leap of faith but here goes with some technical stuff first then a possible solution TANK depending on what other factors come into play on your particular job.

 

The first thing to recognise is that often a wall needs to resist both vertical (from say the weight of a roof or floor)  and lateral wind loading.. even internal walls from time to time as you get different wind pressures occurring inside a building. A big set of bifolds accidently left open say on a windy day. Yes folks,  we need to "have a look" at this possibility "just in case" to make sure the design is safe.

 

In general terms if you take a brick wall (no big windows!) of say 3.0m long with a good return corner of masonry at each end, built off something solid on the bottom, say a foundation and held in place by a stiff roof at the top then the masonry will "span" in two directions.. a bit like a concrete floor slab that is supported on all four sides, you often see these descibed as a "two way spanning concrete slab". However, partly due to the way the bricks / blocks are shaped/ laid a standard UK masonry wall is stronger in the horizontal spanning direction than the vertical direction.

 

Now at 6.0m horizontally that is a long way for a thin wall to span horizontally so it can resist particularly the wind loading.. you don't get much if any help here in terms of horizontal spanning resistance when you come to check the wall is ok. Also, you need to have a look at how the roof is supported on the wall head as sometimes this can cause an unwanted bending effect just to add to your problems.

 

Very simplistically and just to make a corollary. Think of the wall as a series of two beams.. one goes horizontally, one vertically and they both interact and share some of the load. We "know" that a deep steel beam is  often "stronger" than a shallow beam, for example a deep floor joist will often carry more load than a shallow one of the same thickness. The same applies to a masonry wall, the thicker it is then generally the more load it can carry.

 

TANK. At the moment you have a wall with no piers so it's effective thickness is the thickness of the wall assuming it is a single skin. At 6.0m long it's strength is going to come mostly due to it's capacity to span vertically. I think you have recognised that it is probably not quite going to "cut the mustard" especially if you live in a windy area?

 

As a starting point we often say lets put in some piers at 8ft centres ~ 2.4m and see if we can get this to fly. I use imperial units as some of the modern codes still use empirical design to some extent... we know it works! When you put in a pier it often has the effect of increasing the effective thickness of the wall..so in other words you are making the "wall beams" a bit deeper. Now it will carry more load,  and this is how you get it all to work as we have made the wall " effectively thicker" by introducing piers.

 

That's the end of the general  theory bit!

 

Turning back to TANK's issue. It look like there is no enthusiasm for digging up the floor and building up a pier off the founds. Anyway for a retro fitted pier to properly work it needs to be fully bonded into the wall. Ideally, fully bonded also means that both the pier and the wall should be build at the same time. This is because when you lay mortar you need to "tamp it down" so that the bed is evenly compressed for example and bonded to the masonry above and below the bonded in brick/ block. The bricks, blocks of the pier need really to physically interlock.

 

Some may say.. well use a wall starter kit. Fix it to the wall that is built already and build the pier. This does not work as many starter kits have small coach screws with plugs. The ties also can slip vertically so they do not properly bond a remedial pier to the existing wall.. you may as well use wall paper paste. The reason they don't work is that you get an effect called "complimentary shear" this is a vertical force that occurs between the remedial pier and the existing wall. Wall starter kits typically can't resist this force as the ties move up and down within the profile of the wall starter kit.

 

TANK. What about this? Rather than piers go for some wind posts. These could maybe be timbers (or steels) running vertically from the "structural slab" up to the wall head. What you are doing here is splitting the wall up into small panels.. the lateral wind loading is resisted by the timbers and the timbers also stiffen the wall so it can carry more vertical load. Sounds bizarre but.. timbers are cheep. They will stick out from the wall a bit more than steel but you can use them to support the ends of small shelves?

 

Your floor buildup just says "50mm on top of 50mm insulation atop hardcore.)?" I'll assume you have say a 100  to 150  concrete slab under.. if not then.. ? you may have some serious issues with your floor cracking up and nothing to fix the base of the wind posts to.

 

Assuming you do have a solid structural floor slab to connect into. Here is the lastish bits of the puzzle. The floor (structural slab) will go up and down as the moisture content of the ground changes and the loads on the floor vary (call this the "dumpling under the slab") , the walls hopefully will move not so much as the founds will be deeper. How do you connect a wind post to the slab / dumpling that could move up and down? you use a flexible bracket that is "bendy" 

 

https://www.strongtie.co.uk/products/detail/large-reinforced-angle-brackets/265

 

You can't use these brackets above as the the slotted hole (fixing) is too close to the bottom of the wind post if you go for timber, steel usually ok depending on what the profile is but I posted the link to give you an idea as to what might be a "bendy" type bracket! In the world of design it's ok to sometimes let things bend and recover as steel is elastic..your toilet bowl / floor tiles less so!.  So long as you don't go over the score!

 

Now that is a potential solution that will avoid you having to dig a few big holes in the floor to retrofit the piers all the way to the founds. Even if you do you can see that you will have to find a way of properly bonding the pier to the Thermalite.

 

This Thermalite is last elephant in the room.. What you need to do is to find a fixing that will transfer the wind lateral load in the wall to the wind posts. You can often fix brackets to the sides of the timber wind post with square twist nails. You fix the bracket to the Thermalite with an under reamed resin anchor.

 

Attached is the Fischer test report which gives you some pointers as to what fixings can be used in Thermalite blocks, the under reaming drill bits and so on. You can find the drill bits and installation instructions on the web.

 

TANK.. hope this helps. You will probably need an SE to prove this but hopefully it can be a simple process, not too costly compared with BC knocking you back and / or digging up a big bit of the floor in two or three places then making good the DPM and so on.  Even if you do this you'll struggle to bond the new pier in effectively and make a good looking job of it.

 

Even if you don't need this retro work for BC then please be safe and get it (the wall) checked out.

 

For all. The above issues often crop up when you want to knock down a wall along say the back of your house to form an open plan room right along the back of the house. Often you end up with a pier / column of masonry sitting in the middle of the external elevation wall . In the old day windows and doors were made of good solid wood / or metal framed and they stabalised the masonry. Now windows are plastic / aluminium framed with "rubbish" brackets that just don't stabalise the masonry up the sides of the window / door opening. Thus often you need some kind of wind post. Normally this is ok and easyish to do but when you encounter Aerated blocks (Thermalite say) or bricks with holes in them the fixings become an issue.

 

That said often there is a solution.

 

All the best TANK.

 

 

 

 

 

 

 

 

Fischer Test Report for Thermalite_Report(1).pdf

Edited July 21, 2021 by Gus Potter

[saveasteading]

10 hours ago, Gus Potter said:

A few thoughts,

What Gus says is all correct.

Also we don't know enough about your circumstances to give a definitive answer.

 

As it is an outbuilding, you may be allowed/ not silly to under-spec it. If it is very rarely occupied the rules don't always apply, eg garden shed.

 

I don't think it has been mentioned that you might build your pier outside. Then you can take it down to founds. there will be a top ledge that you will have to weather.

 

[TANK]

Thankyou Gus for taking the time to put together such a comprehensive and informative reply. 

Wind posts could work, however, I'm going to take another look at putting in piers. The work involved isn't too difficult providing the is sufficient room on the footing itself, since there is only infill material (soil, hardcore etc) on top of it so far. 

It will just be a nuisance more than anything going back down there since I thought I was done with working at that god forsaken level breaking my back! 

 

Edit :

 

And thank you save. Yes, interesting that you mention external piers, as I just had that thought myself last night. Could be worth a look. 

Edited July 22, 2021 by TANK