Laying out blocks for inner skin of cavity wall

[jamie_]

Hi,

Some background first:

At some point next summer I’m going to lose the room I currently use as a music studio (as I have another baby on the way) so I want to build a decent music shed at the bottom of my garden. Soundproofing is going to be important, so I’ve decided to go with a brick/block cavity wall construction. I’ve got a bit of money saved up for this, but I'm hopefully going to be doing every aspect of the build (except the electrics) myself in order to keep costs down. I’ve got a reasonable amount of experience with most things I’m going to have to do, but my experience of bricklaying is pretty much limited to building a few walls and raised beds etc around the garden. I know enough to do a nice job of it, but I’ve never done a cavity wall.


My question:

I’m currently at the design stage, and trying to draw my shed in Fusion 360 (maybe not the best software for this but I use it in my day job). I was planning to use 300mm wide trench blocks in the foundations and I’ve used a brickwork table to design the outer walls to an exact number of bricks to keep things neat.

My issue is that this leads to dimensions for the internal block walls that don’t work with full sizes of blocks, and I’m not sure what the correct approach is in terms of where I should put any cut blocks along the wall. I understand how to do blockwork corners to maintain a stretcher bond, but if I have to cut blocks to make my walls the right length then what’s the best approach to lay them out? Also do the perps on the blocks need to line up with the perps on the outer skin of brickwork?

I’ve found various documents online relating to laying out bricks, but nothing useful on laying out blockwork.

My shed will be small enough that I won’t need to involve building control, so I’m sure I could just bodge it, but I would still prefer to do it in the proper way (whatever that is).

Any help much appreciated.

Cheers,

Jamie

 

[conny]

Not a brickie but I imagine some of the horizontal joints, (and maybe even some vertical ones), should line up with the brickwork in order to insert wall ties to lock both sets together at various points.

 

[SpecialK]

No the perps don't need to line up. They don't need to be in exact stretcher bond internally. You can cut the block at the end of the runs so they fit.

 

[^woody^]

Same principle as with bricks; cuts in centre of wall or centre of an opening.

But it really does not matter with blockwork that will be hidden, as it's an aesthetic issue not structural.

Do whatever it's easiest, with the least amount of cuts and waste.

 

[Deluks]

If soundproofing is important, cavity wall might not be the way to go.
The wall ties will transmit sound to the external leaf.
You'd be better off making a solid wall, and building a multi layer plasterboarded stud wall internally. The stud wall not touching the external wall.

A speedy way to build the structure would be to use 140mm concrete blocks. Obviously a pig to lay, but they are thick and dense, just like the drummer in your band. ‍

 

[noseall]

If soundproofing is important, cavity wall might not be the way to go.
The wall ties will transmit sound to the external leaf.
You'd be better off making a solid wall, and building a multi layer plasterboarded stud wall internally. The stud wall not touching the external wall.

A speedy way to build the structure would be to use 140mm concrete blocks. Obviously a pig to lay, but they are thick and dense, just like the drummer in your band. ‍

...and then some idiot goes and puts a window in the same room.

 

[robinbanks]

My brother made a shed for an audio engineer friend, scrap log wood outside (the offcut slabs the local saw mill was left with after making a round tree square) , straw fill, double plasterboard inner. Cost virtually nothing compared to the previous studio the guy had, and turned out to be vastly superior from an acoustic perspective.

But as for your block walls, if you persist with that route, just lay them however you like so long as you have 100+mm stagger; you don't need a 220 stagger on a 440 block. If you do want a 220 stagger and you're cutting 330 off a block, You'll be able to use your 110 offcuts somewhere.. concrete blocks can be easily cut with a hammer and chisel, thermalite with a knackered old wood saw (but specific block saws exist too)

 

[robinbanks]

Also do the perps on the blocks need to line up with the perps on the outer skin of brickwork?

Perps are verticals, they never need to line up other than at openings. Beds are horizontal mortar lines. They need to reasonably line up on courses where wall ties are. If you're going to suffer any misalignment, strive to make the inner leaf the slightly higher one so that wall ties are angled sloping downwards towards outside. Don't have a height mismatch where the outer leaf is higher to the extent that you're bending wall ties so the kinks in them no longer drip water off. Also try not to drop large amounts of mortar into the cavity, as a wall tie covered in mortar between inner and outer can track damp across