Help with understanding blocks please....

[r6deano]

Morning all,

Need some help please. I'm researching blocks to buy for my extension.

100mm + 100mm full-fill + 100mm

What's the main purpose for concrete blocks and for aerated blocks? IE does one suit inner/outer skins better?

I'm building off of a building notice so no specs from a SE - will my BCO specific what N rating they will want?

It's a bungalow with a dormer conversion, the inner skin will be supporting a 6 meter steel too.

Block and beam floor - just use concrete blocks?

Also, I'm considering doing both skins in block work and brick slip-ing afterwards (potentially I may external-insulate the existing building of which i could brick slip over, thus all the exterior would match then, rather than the extension brickwork not matching well)

It's worth noting I want the best thermal values for the house too, if that helps select a different block?

Thanks in advance

Deano

 

[tomfe]

Deano if I may ground you a little here. You seem to know very little about building and if you are waiting to build this yourself you are better off reading a lot more before jumping in an asking for help.
All this information is out there, in this forum, on the internet and in books. There are a couple of people who have even made websites detailing their extensions and their thought processes.

If you really don't want to do that get, someone to do the building regulation drawings and follow what they say.

I would do a full fill 150mm cavity med/light block with brick skin. It's also not an N value but a U value. BC do not specify thermal values minimums are 'set' by building regulations.

 

[Doggit]

You use light weight (or aerated blocks) on the inner skin, as they are warmer, but absorb water. You use medium or heavyweight concrete blocks on the outer skin, as they are water resistant and I think it's medium density blocks for the floor. The N value refers to how strong they are. I can't comment on the blocks needed for the steel though.

If the build were doing a normal build, then it'd be light density blocks for the inner skin, and then bricks for the outer skin, but if you intend to externally insulate the property, and then use brick slips, then you'd use concrete blocks for the outer skin instead.

I assume you're doing the extension under permitted development, but you still need a set of plans for Building control, so who's doing the plans and the specs, as these'll be different if you do the EWI now, or later.

 

[mfarrow]

We used light aerated blocks for our floor. Maybe ring the manufacturer and ask them to advise? LiteCast was our manufacturer and 20kg/m @3m meant they were a doddle to put in place.

Use medium concretes on the outer skin, especially if you've not decided on render or slips yet.

As stated, U ratings are from the building regs. look for Approved Documents on PlanningPortal.gov.uk. I think you'll be fine with what you've proposed, but talk through it with BCO on first site visit. Look also at fill manufacturers data, e.g. http://www.knaufinsulation.co.uk/sites/knaufuk/files/downloadfile/3_1_1-masonry-cavity-walls_1.pdf

 

[^woody^]

Why would you want to build in blocks, and then cover with brick slips?

You would only use dense concrete blocks internally if you are building a block of flats. Otherwise you need to use aerated blocks to meet insulation values with minimum fuss.

 

[r6deano]

Deano if I may ground you a little here. You seem to know very little about building and if you are waiting to build this yourself you are better off reading a lot more before jumping in an asking for help.
All this information is out there, in this forum, on the internet and in books. There are a couple of people who have even made websites detailing their extensions and their thought processes.

If you really don't want to do that get, someone to do the building regulation drawings and follow what they say.

I would do a full fill 150mm cavity med/light block with brick skin. It's also not an N value but a U value. BC do not specify thermal values minimums are 'set' by building regulations.

Hi fella,

Appreciate the advice. I have a family friend that has built plots for most of his life, so he is throwing contacts my way as I go into each stage. I'm an avid DIY-er so want to be able to get my hands dirty where I can, knock up, labour, plan, etc etc but leave the technical bits like fitting the steels and new roof to those with the skills

No doubt he will tell me the blocks to buy. Just I love a bit of research and understanding thus the post.
When I say N values I meant as in 3.6Newtons /7.2 for the bloc spec - wondered if certain strengths had to be used for supporting walls or steels?

I've read a couple of those home made sites they keep my buzz going (!)

I have a tendency to over engineer things so any advice greatly appreciated.

Thanks again!

 

[r6deano]

You use light weight (or aerated blocks) on the inner skin, as they are warmer, but absorb water. You use medium or heavyweight concrete blocks on the outer skin, as they are water resistant and I think it's medium density blocks for the floor. The N value refers to how strong they are. I can't comment on the blocks needed for the steel though.

If the build were doing a normal build, then it'd be light density blocks for the inner skin, and then bricks for the outer skin, but if you intend to externally insulate the property, and then use brick slips, then you'd use concrete blocks for the outer skin instead.

I assume you're doing the extension under permitted development, but you still need a set of plans for Building control, so who's doing the plans and the specs, as these'll be different if you do the EWI now, or later.

Thanks for that info Doggit.
The extension is being done via a building notice. The EWI I would only apply to the current building that is not being renovated at a later date.

 

[r6deano]

We used light aerated blocks for our floor. Maybe ring the manufacturer and ask them to advise? LiteCast was our manufacturer and 20kg/m @3m meant they were a doddle to put in place.

Use medium concretes on the outer skin, especially if you've not decided on render or slips yet.

As stated, U ratings are from the building regs. look for Approved Documents on PlanningPortal.gov.uk. I think you'll be fine with what you've proposed, but talk through it with BCO on first site visit. Look also at fill manufacturers data, e.g. http://www.knaufinsulation.co.uk/sites/knaufuk/files/downloadfile/3_1_1-masonry-cavity-walls_1.pdf

More great info, thank you!

I'm considering maybe a Jetfloor/Litecast GT block and beam construction for the ground floor. Quotes on their way!

 

[Doggit]

Having seen the benefits of EWI, I'd think about doing it with the build, and then using brick slips for the finish. The EWI will help you achieve a very low U value, and you'd be using concrete blocks for the outer skin, so this'd go up quickly, save on labour and material costs, and offset the EWI costs.

 

[r6deano]

Why would you want to build in blocks, and then cover with brick slips?

You would only use dense concrete blocks internally if you are building a block of flats. Otherwise you need to use aerated blocks to meet insulation values with minimum fuss.

Would you know what blocks / rating you'd use internally if a steel is going in?

Thanks woody. Defo stick to the bungalow for now, maybe flats in a couple of decades ...

I was considering build in blocks then cover with slips for a couple of reasons-

1) if a block Covers approx 6/7 facing bricks, and are both just over a £1, then assuming I could get 6/7 slips plus the cost of one block to equal the cost (or close to) of 6/7 facing bricks, the cost is similar. Less labour on the blocks, but added labour on the slips (although I'd happily attempt 'tiling' the slips as opposed to laying facing bricks!)

2) the extensions' new brickwork will no doubt stick out against the existing. As will any brick slips I may add at a later date if I EWI. So doing it all now would give a nice uniform blend all round.

3) building in blocks then slipping is something I could do a lot of myself. Not to save money, just to feel involved and put my stamp on it.

Thanks again!

 

[r6deano]

Having seen the benefits of EWI, I'd think about doing it with the build, and then using brick slips for the finish. The EWI will help you achieve a very low U value, and you'd be using concrete blocks for the outer skin, so this'd go up quickly, save on labour and material costs, and offset the EWI costs.

Given I'm probably going to give an Air Source HP a try, maximum thermal efficiency is a must. Cheers !

 

[noseall]

1) if a block Covers approx 6/7 facing bricks, and are both just over a £1, then assuming I could get 6/7 slips plus the cost of one block to equal the cost (or close to) of 6/7 facing bricks, the cost is similar. Less labour on the blocks, but added labour on the slips (although I'd happily attempt 'tiling' the slips as opposed to laying facing bricks!)

Jesus Christ! For the love of God - hire a brickie. Who would want a house clad in brick slips for heavens sake!!

 

[Doggit]

With a ground source heat pump, you're picking up the stored warmth held in the ground that's a fairly similar temperature all year round, but as Air Source heat pumps are trying to extract heat from a rising and falling outside air temperature, the coefficient of efficiency is undeterminable. Okay for autumn, crap for winter. The other benefit of a ground source pump, is that you can reverse some systems in the summer, and get air conditioning.

 

[r6deano]

Jesus Christ! For the love of God - hire a brickie. Who would want a house clad in brick slips for heavens sake!!

Am I wrong in assuming they look exactly the same as facing bricks then? Thought many were 20mm slices of bricks anyway? Plus if you read above you'll see I'm considering EWI so I'd have to slip em to keep on with the neighbours.

Think you're missing the point that it's not I don't want to hire a brickie - I want the satisfaction of doing as much as possible. I was having a brickie but he let me down so now I'm exploring other options. I find your comment a tad rude Mr Noseall! This is a site for DIY enthusiasts - plenty of nicer ways to suggest alternatives.

 

[Doggit]

The problem with bricks slips deano, is that you need to be pretty good at pointing. The manufacturers suggest using a Pointmaster to pump in the mortar, and then use a rake to finish off. The problem is you need to be pretty experienced to get the mortar mix right; too wet, and the Pointmaster just squeezes out water, to dry, and nothing comes out. It's very easy to ruin the face of the slips by getting cement on them. And I know because my pointing crap.