Designing to brick/block dimensions and expansion joints/piers

[Pabbles]

Hi everyone.

 

I'm in the process of redesigning a detached garage, which we're hoping to start building in the coming weeks.

 

After a few poor experiences with an architect, we (builder and I) ended up taking on the planning process ourselves. I owe him a redraft. We'll obviously run the plans past our private building control inspector before starting, but its a bit of a chicken and egg scenario: I need to finalise the plans to agree a price so I know we can go ahead... and then keep a little back for the inevitable alterations BC require,

 

I have three tasks:

 

1) Rescale the drawing to suit standard brick and block dimensions (i.e. make it slightly bigger where necessary to reduce the number of cut brick/blocks required.

2) Consider the inclusion of block piers on the internal skin.

3) identify expansion joints.

 

The high-level draft plan is attached - currently at a nominal 11.5 x 8m footprint. Construction is cavity wall over trench-blocks/engineering brick, with a 65 x 215 x 102.5 mm facing bricks and 440 x 100 x 215mm dense concrete blocks on the inner course. 100mm (97.5) cavity.

 

I've been redrawing the building in CAD (my happy place) - have modelled every brick and roof component so that I can accurately assemble it on the computer and produce accurate drawings and materials lists.

 

I have a few questions if anyone would be good enough to answer?:

 

1) When I try to rescale the building according to the brick and block dimensions, there isn't an obvious size. If I scale it so that the bricks don't need to be cut, then the blocks do need to be cut (and vice versa) and when I lay out the trench-blocks in CAD (440mm tongue and groove) then they always need to be cut to suit the blockwork above (the tongue and groove means no 10mm mortar bond on the sides which throws the standard dimensions out). I believe it is not possible to have a size that will suit all three brick./block dimensions and that there is therefore a compromise needed. Would anyone be good enough to suggest a size I should aim for (at or above the 11.5m x 8m initial plan) that would minimise the bricklaying labour in terms of cuts and adjustments?

 

2) We did have a structural engineer involved. This was due to an initially complex inner roof structure. His suggestions were OTT - more steel than Wembley stadium, we quickly moved to a truss design to avoid his doubling the budget. However he did suggest that the building needed four 440 x 140mm block piers on the inner course, one each on the north, south, east and west walls. The pier on the south wall (the one with the doors) was located offcentre, between the vehicle doors and the one on the North wall was directly opposite, again offcentre. The main purpose of these piers was to support some massive steel beams, which have since been removed from the plan (part vaulted ceiling to allow for a car lift, our local truss company came up with a much cheaper and more elegant solution - see the attached image from our CAD model, you can see the part-vaulted section clearly). So, while the piers are no longer needed to support the steels, I'm sure they would still be necessary due to the length of the walls. Can anyone comment on whether we still need all four piers of would two on the long walls only suffice? We have no issue with the cost of the piers, more that it impacts floorspace.

 

3) Finally. The structural engineer did suggest movement joints would be needed due to the span of the walls, but these aren't included in his drawings. I have read the designing for movement in brickwork technical guide but this seems to suggest that expansion joins are only needed every 10-12m (15m max) horizontally and 9m vertically. As such, it doesn't seem like they are needed. Could anyone offer any guidance here? Again, cost isn't a factor, rather in this case it is aesthetics. The building is being put up using reclaimed-style brickwork (newly made from Imperial bricks) and the styling is intended to mirror the local barns so we don't want to have visible expansion joints if they aren't needed.

 

Many thanks indeed for reading and thanks in advance for any help.

 

 

Edited December 6, 2023 by Pabbles

[Russell griffiths]

I have only read the first little bit, as I basically couldn’t be bothered. 

However being an ex bricky I hope I can help a bit. 

You will not have any cut bricks, none, don’t do it. 

Work it out in brick sizes exactly on the exterior face. 

if you need movement joints then put them exactly in the middle of a brick so the wall basically stops and starts as if it was two independent walls. 

 

All of the above is based on you using basic stretcher bond. 

 

Block work will have to fit accordingly, block work is secondary it’s the brickwork that needs to look right. 

[DevilDamo]

Surely your post can be summarised sowhat is the issue or what are you trying to achieve?

[George]

1) use this chart for brick dims

 

https://www.wienerberger.co.uk/content/dam/wienerberger/united-kingdom/marketing/documents-magazines/technical/brick-technical-guidance-sheets/UK_MKT_DOC_Brickwork%20Dimension%20Tables.pdf

 

2) probably not if it's a cavity wall but it depends on the location. Brick piers are usually used on single skin walls to increase the effective thickness.

 

3) you probably won't need MJs in the brickwork as it's less than 12m. But as a safeguard I'd use a M4 mortar with hydrated lime and cement. 

 

If you wanted to be sure you could add bed joint reinforcement every third course... I'd rather do that than put MJs in external leaves.

 

The blockwork inner leaf will need them. 2 in the back wall, 3m from the corner and 1 in each side wall placed centrally. These should use slip ties.

 

Fee £300 please 

 

 

Edit - just a thought, there could be a significant point load from the girder trusses, did the truss manufacturer give any guidance on what support was needed? I'd suspect not so potentially you'd need piers to support those.

 

 

Edited December 6, 2023 by George

[Pabbles]

SUMMARISED (thanks @DevilDamo):

 

You are all quite right, that post was far too long - I do apologise. It looked smaller on the laptop but was a tome when I read it back on my phone.

 

So, for brevity:

 

• Question 1: when designing a brick/block building, it it better to set building dimensions based on full bricks, full blocks or full trench blocks?
• Answer: From @Russell griffiths: Base it on full facing bricks and cut the blocks to suit.
• Supporting answer from @George: Use the Weinerberger chart for standard brick dimensions.

 

• Question 2: From my drawing, do I need internal piers, external piers or both?
• Answer: Inferred from @George, not on the outer skin. Possibly not needed at all due to cavity construction. Did the roof truss company specify a pier under the two girder trusses? (its actually four, each pair is of double truss construction). No they didn't the whole design was shown sitting on the timber wall plate.
• Outstanding question: are there any published standards for the size/frequency of piers on the internal leaf of a cavity wall?
• Sensible thought, based off feedback from @George: putting 2x piers on each 11.5m wall (4x piers in total) directly under the girder truss pairs might kill two concerns in one.

 

• Question 3: do I need movement joints as the specs seem to say every 12-15m?
• Answer: from @George, probably not.
• Suggestions from @George and @Russell griffiths: consider the type of mortar chosen and whether to include bed joint reinforcement.

[Russell griffiths]

I’m a bit more interested now as I’m sitting down with a cuppa in my hand. 

 

A couple of random thoughts. 

 

That is a big footprint to build, just for a garage, it could be built much cheaper in single skin, or timber clad. 

But you have gone cavity and a car lift, so it’s probably somewhere you will spend a bit of time, so it’s going to be an expensive garage to build with the size and construction method. 

 

How about going higher and putting an annex upstairs, I bed annex or granny flat. Home office, gym. 

Chuck 25 grand more at it. 

 

 

Around here it would rent out for £800 a month, that pays a lot of mortgage. 

 

Construction wise i might look at something else. 

Cavity construction is very poor insulation wise, unless you up the spec to meet current house regs. 

So if you want a warm garage you will need to build it to building regs standard. 

 

If your happy with a cold garage then you could look at a lightweight steel frame with a brick outer skin, if all the bricks are for is making it look like the surrounding buildings. 

 

You could put some steel windposts in the block wall if you didn’t want piers, they could take the load of the girder trusses and prevent the long length of wall from getting the wobbles, but I’m not an engineer that’s up to blokes like @George who I believe are. 

 

Lots of ways to skin this cat. 

[Pabbles]

Thanks Russell. Yes - it’s a bit of a dream of mine. We bought the house specifically because the layout of the land lent itself to a lot of outbuildings under PD (about an acre in an L shape with no neighbours).

 

Our local authority planning team have been overwhelmed for many years, even the pre-planning advice team is shut down, so this design is quite specifically chosen to sit within permitted development regs (2m from boundary, 4m ridge, 2.5m eaves and less than 50% of the curtelage) so that we don’t need planning - but do need building regs. Seems ridiculous we can build something so large, but that’s the law.

 

I'm a quite passionate classic car builder so the garage is a real workplace for me. It will  also have an office in there for my day job. We’re lucky enough to already have a dedicated gym building so no real need to go higher and we’re loathed to start going through planning.

 

the brick facing is important as it ties in with the area (lots of larger barns of similar construction) so will help with resale if we ever sell (not expecting to recoup the full costs but, for example, a steel clad or rendered building would hamper not help the value).

 

I’m very much open to ideas on how to reduce the costs while keeping the brick fascia if you have any? Solid wall is obvious but that’s more brick. Single skin would be cold and less robust. Softwood is out due to longevity. I would have looked at ICF if I’d been happy with render. Steel building was my first choice and they’re cheap… unless you want any sort of insulation at which point the price gets absolutely ridiculous and brings it in line with brick/block construction that will last far longer. Even oak was cheap compared to insulated steel.

 

there is still a tight budget, but I think (subject to me planning every brick on CAD  to remove the estimating contingency) we can pull it in on plan.

Edited December 8, 2023 by Pabbles

[Brickie]

Couple of thoughts (apologies if I’m repeating anything @Russell griffiths or anyone has said-skipped through the thread)-

1/ you’re overthinking,the runs are long enough that the perp joints could be opened or tightened slightly to make it work bricks,especially if they are ‘new’ imperials-likely to be longer than 215mm. Just make the piers brick dimensions I.e 890mm,1340mm etc but check brick dims with your manufacturer. 
2/ unless you’re footing is going to spot on forget about trench blocks. 
3/ if it’ll work for the maximum lengths,hide the mj’s round the corners behind the down pipes from the roof.