New Kitchen/Living extension. Brick & block or brick and timber?

[Triggaaar]

Hi all

 

We've just applied for planning permission for a single story extension in Brighton, and if it passes (and we can get the money) I'd like to start with build as soon as the worst of the winter is over.

 

That means trying to get quotes as soon as I can, which means trying to make decisions now.

 

We were originally thinking of brick and block, but to improve the insulation we're now thinking of brick, then timber stud with insulation in-between, and further insulation inside it.

 

Here are the proposed elevations:

 

The plan is for the finished room to be 7.6m wide x 9.2m long, 2.8m high (internal). The East elevation will be mostly glass, so brick & block or brick & timber doesn't have so much affect.

The South elevation will be a completely new wall (9.2m internal), and hopefully it will butt right up to the existing boundary brick wall (which is about 6'6" high).

The north elevation wall is mostly already there - we'll need to build a little on top, or knock some of it down and rebuild, I don't know.

 

Any suggestions on the pros and cons of brick & block (with Rockwool in-between) vs brick & timber stud would be much appreciated.

 

Thanks

[PeterW]

For the sake of differential movement I would go with brick and block everywhere. Footings will be the same regardless and if you’re building on a boundary it will be quicker as the outer skin can go up at the same time as the inner blockwork. 

 

What concerns me is the roof span as there are no internal supports. That is going to need some serious work with either steels or very big timbers. You’re on the edge of the capability of a 373/146 posijoist at that span and potentially need to go to a 416/122 which are huge - and expensive ..! What has your architect / SE planned for the roof ..?

[Triggaaar]

29 minutes ago, PeterW said:

For the sake of differential movement I would go with brick and block everywhere. Footings will be the same regardless and if you’re building on a boundary it will be quicker as the outer skin can go up at the same time as the inner blockwork.

 

Thanks. I mentioned to the architect that I want to exceed the building regs insulation requirements, so that the room stays warm with little heating, so he suggested timber studwork inside the bricks. How do you think we could improve the insulation if we go brick and block?

 

 

29 minutes ago, PeterW said:

What concerns me is the roof span as there are no internal supports. That is going to need some serious work with either steels or very big timbers. You’re on the edge of the capability of a 373/146 posijoist at that span and potentially need to go to a 416/122 which are huge - and expensive ..! What has your architect / SE planned for the roof ..?

 

Are posi-joists the zig-zag timber/metal beams? We were thinking of a large steel universal beam across the width of the kitchen, supporting the room above. Getting it in, almost by hand, will be a challenge. One option is to have it in 4 pieces - instead of one length of 8m (ish), a 5m & 3m piece joined together, running parallel with and attached to a similar pair, 3m & 5m, so the joins don't overlap. This is pure guesswork at this stage, as the architect won't know until he asks his engineer. Then a steel from that back towards the house, to support the side wall of the room above. If that can't be done, we'll have to have a supporting steel column part way along the length.

Then we'd also need an 8m ish steel over the sliding glass doors. And possibly a third too (one issue I have is allowing for roller blinds fitting into the ceiling). Then we'd just have standard timber joists between the steels.

 

The long posi-joists are something I've seen on tv, and plan to ask the architect about, in case we can use them (as well as some steel, which is unavoidable).

[PeterW]

1 hour ago, Triggaaar said:

Are posi-joists the zig-zag timber/metal beams? We were thinking of a large steel universal beam across the width of the kitchen, supporting the room above. Getting it in, almost by hand, will be a challenge. One option is to have it in 4 pieces - instead of one length of 8m (ish), a 5m & 3m piece joined together, running parallel with and attached to a similar pair, 3m & 5m, so the joins don't overlap. 

 

Sorry I’m lost here ...

 

Are you saying there is an opening at the end of the house so the extension will extend an existing room ..? So you want to support both back walls to create an opening ..?

 

 

8m steels to support the back of the house will probably need to be 356x127x39 so they will be 320kg each. Splicing those will need some serious work so you may need to go even deeper...

 

You can just about span the 8m with just roof loads using a 254x146x43 and it may be better just spanning the whole build 3 times and then using timber between the flanges. It would be quicker and possibly cheaper. 

 

The SE really needs to get a good idea of what you need as if not, you could end up with some nasty drops in the ceiling where the steels go

[Triggaaar]

Just now, PeterW said:

 

Sorry I’m lost here ...

 

Are you saying there is an opening at the end of the house so the extension will extend an existing room ..? So you want to support both back walls to create an opening ..?

 

It's currently a typical Victorian/Edwardian house, where the kitchen extends into the garden, but not at the full house width, giving you a side return. We want to knock down the existing kitchen walls (rear wall, as side wall), and extend into the side return, and also further into the garden (there is currently a conservatory into the garden, but for the sake of understanding the plans, we can ignore that).

 

Just now, PeterW said:

8m steels to support the back of the house will probably need to be 356x127x39 so they will be 320kg each. Splicing those will need some serious work so you may need to go even deeper...

 

You can just about span the 8m with just roof loads using a 254x146x43 and it may be better just spanning the whole build 3 times and then using timber between the flanges. It would be quicker and possibly cheaper.

 

Quicker and cheaper sounds great to me

So you mean steels with a cross section of 254x146x43, and putting timber joists between them? That would be fine at the back of the extension, but we'd still need something big to support the existing first floor and roof (a 320kg steel sounds reasonable, I was concerned it would be more).

 

Just now, PeterW said:

The SE really needs to get a good idea of what you need as if not, you could end up with some nasty drops in the ceiling where the steels go

 

I'm hoping we'll be ok with flat ceilings. The existing kitchen ceiling is around 3.15 / 3.2m high, and we're after a finished ceiling of 2.76m, so there should be room for the steel.

 

Thank you for the help

[Triggaaar]

I met the architect again today, and mentioned the concern of different expansion rates if we go timber on the inside, with brick/block on the outside, and he said it wasn't a problem, and was common these days. If we do go that route, my main concern it being able to build a brick/block wall up to an existing brick boundary wall, and at the same time building a timber wall on the inside, and joining the two with wall ties:

 

There would only be a 50mm cavity between the bricks and the Tyvek/ply/studs, which means we'd need to build the stud wall first, then put 600mm strips of ply in place (with rolls of Tyvek in the way), then reach over to lay the bricks and add ties, before doing the next strip of ply. Meaning just 6" space between the ply and the existing brick boundary wall, to get fixings in (from ply to timber stud).

 

I wondered if instead we could build the brick block wall up to 7 feet (matching the boundary wall), and then build the timber studs with ply and Tyvek, flat on the ground, then stand it up and then add wall ties, drilling them in to the finished brick/block wall? I don't know if that's an acceptable method or not. Perhaps it would be good if the outer skin were concrete blocks, meaning we'd likely get a good fixing?

 

Any ideas?

 

Thanks

[Declan52]

Unless you have arms like inspector gadget you aren't going to be able to get enough wall ties screwed in.  The wall ties go in every 450mm high so no chance you will be able to reach down and put enough in.

If your that close to a boundary wall then brick and block will be the easiest method. 

[Triggaaar]

Thanks for the reply.

 

5 minutes ago, Declan52 said:

Unless you have arms like inspector gadget you aren't going to be able to get enough wall ties screwed in.  The wall ties go in every 450mm high so no chance you will be able to reach down and put enough in.

 

Can't we build be wall, drill through the ply and into the brick, and insert wall ties?

 

5 minutes ago, Declan52 said:

If your that close to a boundary wall then brick and block will be the easiest method. 

 

Yes it does sound easier, but I'm concerned about getting enough insulation in. Any suggestions?

[Declan52]

45 minutes ago, Triggaaar said:

Thanks for the reply.

 

 

Can't we build be wall, drill through the ply and into the brick, and insert wall ties?

 

 

Yes it does sound easier, but I'm concerned about getting enough insulation in. Any suggestions?

Have you seen any kind of wall ties that would be suitable for what you are planning??? 

Doing a build is hard enough to do so try to make every stage as easy as you can.  For what you are looking brick and block will be the easiest.  If the boundary wall will be the same height as your wall then you can use blocks as they will never be seen.  Any where that will be visible you can build it in brick if that's the finish you want. 

As  for insulation just make the cavity 150mm,175mm,200mm,300mm. Pick one that suits what you want to end up with.  More insulation means  more heat kept in the house but more cost.  So work out what suits the budget and run with that.  The wider the cavity the more attention you need to pay to the window and door junctions.  Cavity closers or return the block work will be your option. 

As for the type of insulation that you could put in the cavity I would go with eps beads blown in to fill the cavity.  You  can also go with  rock wool type materials.  Have a chat with your architect and see what he thinks will suit your needs on your site. 

[Triggaaar]

38 minutes ago, Declan52 said:

Have you seen any kind of wall ties that would be suitable for what you are planning???

 

No But isn't a wall tie basically just a piece of metal, so wouldn't some large screw work?

 

 

38 minutes ago, Declan52 said:

Doing a build is hard enough to do so try to make every stage as easy as you can. For what you are looking brick and block will be the easiest.

 

Understood. I can't lay bricks, I'll need someone in for that. But I've known my chippie for decades and can do studwork with him for less than bricklaying costs, so if there was a sensible brick/timber solution, I'd like to go with it, but I understand we may be better with brick/block.

 

38 minutes ago, Declan52 said:

If the boundary wall will be the same height as your wall then you can use blocks as they will never be seen.  Any where that will be visible you can build it in brick if that's the finish you want.

 

Our wall will be about 3.3m high, and the boundary wall is about 2m high. I was thinking of blockwork up to the height of the boundary wall, and then brick above so it looks ok for the neighbour.

 

38 minutes ago, Declan52 said:

As  for insulation just make the cavity 150mm,175mm,200mm,300mm. Pick one that suits what you want to end up with.  More insulation means  more heat kept in the house but more cost.  So work out what suits the budget and run with that.  The wider the cavity the more attention you need to pay to the window and door junctions.  Cavity closers or return the block work will be your option.

 

Well since the wall is up against the boundary, we'll have no doors or windows there. We just have to sort out the detail where the wall turns 90 degrees, and then meets the sliding glass doors.

 

38 minutes ago, Declan52 said:

As for the type of insulation that you could put in the cavity I would go with eps beads blown in to fill the cavity.  You  can also go with  rock wool type materials.  Have a chat with your architect and see what he thinks will suit your needs on your site. 

 

I'd not thought of filling the cavity with beads. The architect was just suggesting a 2" gap and then some Celotex, and then more on the inside too if I wanted (as he felt it would be harder to build the wall well with a large cavity (allowing for wall ties etc).

 

I was planning on a wall thickness of 12" - could go a couple more inches for improved insulation, but I don't want to eat into the room if I don't have to. That's why we thought brick and timber would work.

 

Thanks you for all the help, much appreciated

[PeterW]

3 hours ago, Triggaaar said:

 

I met the architect again today, and mentioned the concern of different expansion rates if we go timber on the inside, with brick/block on the outside, and he said it wasn't a problem, and was common these days.

 

 

It is .... for timber frame new builds ..! The whole house shrinks and the expansion gaps in the window heads and other openings take up the slack. 

 

Ask him how he wants to detail the flat roof upstand junction with the main house to allow the timber frame to drop by 20mm with shrinkage and not tear the membrane roof..? 

[Triggaaar]

1 hour ago, PeterW said:

 

It is .... for timber frame new builds ..! The whole house shrinks and the expansion gaps in the window heads and other openings take up the slack. 

 

Ask him how he wants to detail the flat roof upstand junction with the main house to allow the timber frame to drop by 20mm with shrinkage and not tear the membrane roof..? 

Thanks for the warning, I'll ask him. That's why I'm asking questions on here, rather than just assuming what he says will work

 

[Triggaaar]

On 13/11/2018 at 19:40, Declan52 said:

As  for insulation just make the cavity 150mm,175mm,200mm,300mm. Pick one that suits what you want to end up with.  More insulation means  more heat kept in the house but more cost.  So work out what suits the budget and run with that.  The wider the cavity the more attention you need to pay to the window and door junctions.  Cavity closers or return the block work will be your option. 

As for the type of insulation that you could put in the cavity I would go with eps beads blown in to fill the cavity.  You  can also go with  rock wool type materials.  Have a chat with your architect and see what he thinks will suit your needs on your site. 

 

Could you tell me more about using eps beads please? The pros and cons, and what size cavity suits its use. Same for using rockwool or Celotex - I don't know the pros and cons of each option.

 

I haven't yet asked him about the problem of timber shrinking, as I just think he'll say it won't be a problem, but then he's not the one who has to deal with any problems if it does.

 

We've considered brick and block, and brick and timber (both of which seem to have issues for us) - should we also consider Insulated Concrete Formwork (ICF)?

Could we just install an ICF wall up against the boundary wall?

 

Thanks

[Declan52]

The width of the cavity will be determined by what you want to end up with.  Some installers use graphite beads which will give you a better overall u value which means you can have a narrower cavity.  You will have to contact the various companies near you to find out what beads they do and then what width will meet building regs. If you want the house warmer then the cavity will have to be wider,150mm at a min but that's up to you.  Beads will be blown in under high pressure so fill every single gap.  As they are covered in glue they set in the cavity to form a single lump with tiny holes for any water that gets in from the outside to trickle down to the bottom. 

Rockwool and cavity boards you are at the  mercy of the guy putting them in.  If they don't get put tight to the wall then heat escapes and the expensive insulation is worthless.  With  Rockwool drops of motar can leave air gaps as well. 

Icf would work as well.  How is access as you will need lots of concrete and a big pump. 

[the_r_sole]

.

Edited September 26, 2019 by the_r_sole

[Triggaaar]

1 hour ago, Declan52 said:

The width of the cavity will be determined by what you want to end up with.  Some installers use graphite beads which will give you a better overall u value which means you can have a narrower cavity.  You will have to contact the various companies near you to find out what beads they do and then what width will meet building regs. If you want the house warmer then the cavity will have to be wider,150mm at a min but that's up to you.  Beads will be blown in under high pressure so fill every single gap.  As they are covered in glue they set in the cavity to form a single lump with tiny holes for any water that gets in from the outside to trickle down to the bottom. 

Rockwool and cavity boards you are at the  mercy of the guy putting them in.  If they don't get put tight to the wall then heat escapes and the expensive insulation is worthless.  With  Rockwool drops of motar can leave air gaps as well.  

 

You make the eps beads sound really good. I am concerned about how well a brickie would  install the insulation (my experience of this dates back a while, and they had little interest/knowledge of insulation, I expect they're better now), so beads being pumped in sounds good.

What we want:

Insulation - the room is going to be the most used room of the house, so I'd like it to be fairly well insulated, and I just figured I'd probably want to do more than building regs (no science there, just a hunch). I guess there's no point going crazy, as 4 metres of outside wall will be part of the original house, which won't fair so well.

Cost - I can't throw tons of money at it, so I'd want most of the extra spending in upgrading the insulation to get paid back in fuel savings over the years (tough to quantify). Is the cost of using eps beads similar to the other methods?

Width - block and brick with a 150mm cavity would be about 14.5" total, which would be ok. Maybe a little more, but I wouldn't want much more room space going. I assume brick and timber would allow us to have good levels of insulation without much wall thickness.

 

1 hour ago, Declan52 said:

Icf would work as well.  How is access as you will need lots of concrete and a big pump. 

 

The extension is at the back of the house, so it would have to be pumped down the side path, 30 metres.

 

Thank you for the help, much appreciated.

 

[Triggaaar]

1 hour ago, the_r_sole said:

I've heard this argument a few times on this forum in the few weeks i've been a member - I've done lots of timber frame extensions onto either stone or brick buildings - you always attach bearers into the existing walls which are never going ot shrink by 20mm on a single storey extension unless you are using green timber or something?

What do you mean by 'attach bearers into the existing walls'?

 

 

1 hour ago, the_r_sole said:

However, the elephant in the room here, is that with those spans there is going to be significant steel work required which, if you go with timber frame, will need posts to be taken down to pads and you either then have a weak point in insulation terms or you box around them

Yes, if we went for brick on the outside and timber inside, we'd have steel posts from the beams to the foundations. The plan was to have about 90mm Celotex between the joists, and then another 75mm ish on the inside - so the steel columns would only have 75mm inside of them. There may only be 2 steel columns to worry about though - one each end of the main girder. Because the steel at the end of the room would be past the glass doors (there's a 500mm ish overhang). So would that be ok?

 

1 hour ago, the_r_sole said:

as a big fan of timber frame and non traditional construction, this one looks like traditional all day long

 

Thank you for the advice, much appreciated. If we went brick and block, how would you go about insulation?

 

[Declan52]

43 minutes ago, Triggaaar said:

 

You make the eps beads sound really good. I am concerned about how well a brickie would  install the insulation (my experience of this dates back a while, and they had little interest/knowledge of insulation, I expect they're better now), so beads being pumped in sounds good.

What we want:

Insulation - the room is going to be the most used room of the house, so I'd like it to be fairly well insulated, and I just figured I'd probably want to do more than building regs (no science there, just a hunch). I guess there's no point going crazy, as 4 metres of outside wall will be part of the original house, which won't fair so well.

Cost - I can't throw tons of money at it, so I'd want most of the extra spending in upgrading the insulation to get paid back in fuel savings over the years (tough to quantify). Is the cost of using eps beads similar to the other methods?

Width - block and brick with a 150mm cavity would be about 14.5" total, which would be ok. Maybe a little more, but I wouldn't want much more room space going. I assume brick and timber would allow us to have good levels of insulation without much wall thickness.

 

 

The extension is at the back of the house, so it would have to be pumped down the side path, 30 metres.

 

Thank you for the help, much appreciated.

 

There is a heat loss spreadsheet on the forum that you can put in all the different types of wall construction and cavity widths and see where your sweet spot is.  You will need prices of Epson beads, rock wool, cavity boards etc to figure it out though. 

[Triggaaar]

So there seems to be something of a consensus, suggesting I go for brick and block. Sounds good to me.

 

I've just been reading through this thread, which looks at the insulation options for blockwork:

 

On 10/11/2018 at 17:21, PeterW said:

For the sake of differential movement I would go with brick and block everywhere. Footings will be the same regardless and if you’re building on a boundary it will be quicker as the outer skin can go up at the same time as the inner blockwork.

 

I see you posted on the thread above, and you went for:

150mm Cavity

Graphite blown bead

25mm PIR between battens 

 

Why did you add PIR on the inside, as opposed to just using more blown bead in a wider cavity? Is it better per inch, or more affordable, or did you really do it to make running cables easier?

 

Do you get a specialist in to do the beads, once the roof is on with the cavity sealed at the top?

 

Thanks

[PeterW]

6 minutes ago, Triggaaar said:

 

 

I see you posted on the thread above, and you went for:

150mm Cavity

Graphite blown bead

25mm PIR between battens 

 

Why did you add PIR on the inside, as opposed to just using more blown bead in a wider cavity? Is it better per inch, or more affordable, or did you really do it to make running cables easier?

 

Do you get a specialist in to do the beads, once the roof is on with the cavity sealed at the top?

 

Thanks

 

The 25mm PIR helped with two things - the uValue is increased by a fair bit and it made the wiring really easy - we chased 3 back boxes in total. 

 

Cavity bead is blown from the inside after it’s watertight as you need the cavity closers in. 

[Triggaaar]

11 minutes ago, PeterW said:

 

The 25mm PIR helped with two things - the uValue is increased by a fair bit

Thank you. Is the uValue increased by more than an extra inch of cavity with beads?

Edited November 16, 2018 by Triggaaar

[PeterW]

17 minutes ago, Triggaaar said:

Thank you. Is the uValue increased by more than an extra inch of cavity with beads?

 

Yes it’s about 40% increase on the equivalent value. 

[Triggaaar]

1 minute ago, PeterW said:

 

Yes it’s about 40% increase on the equivalent value. 

I didn't word my question well - so the uValue is better having 25mm of PIR inside (and 150mm beads filled cavity), that having a 175mm bead filled cavity - which begs the question why not make it a 125mm bead filled cavity, and have 50mm of PIR inside?

[PeterW]

No reason not to other than cost and complexity. 

 

25mm fits perfectly between standard roofing battens which were fitted to the walls at 400mm centres and the insulation cut to be a push fit. If you go to 50mm then you will need double the timber thickness plus the insulation will be more expensive.  

[Triggaaar]

6 minutes ago, PeterW said:

No reason not to other than cost and complexity. 

 

25mm fits perfectly between standard roofing battens which were fitted to the walls at 400mm centres and the insulation cut to be a push fit. If you go to 50mm then you will need double the timber thickness plus the insulation will be more expensive.  

Thanks. So having your 25mm of PIR was more expensive than another 25mm of cavity and beads, but it was worth it for the better uValue and ease of running cables. All sounds good. I'll suggest the architect puts this in the plans.

Would I need a specialist to fill the cavity with beads? Presumably they drill holes in the finished blockwork, and once they're done I can install the PIR?

Edited November 16, 2018 by Triggaaar