How to build interior wall?

[Sophon]

I have a question, but I'm not sure anyone here will be able to answer it since it probably requires some engineering or construction background. But nothing ventured, nothing gained..

We are in the process of building a house in Lamphun. All exterior walls will be build with 20 x 20 x 60 cm AAC blocks, and for interior walls (except for bathrooms) we will be using 10 x 20 x 60 cm AAC bocks. So far so good. However, we want to extend the kitchen, which in the original plans was 3 x 3 m by another meter.

Floor plan:

Originally all walls was directly above and being supported by beams, but the change in plan will put this kitchen wall one meter away from the beam originally intended to support it.

Beam structure:

The floor is constructed of pre-constructed CPAC 4 m x 60 cm x 5 cm concrete planks, with an extra 5 cm of concrete poured on top of that. The wall in question is running almost exactly down the middle of one of these concrete planks. The question is, what materials to use for this particular wall; 10 cm AAC blocks or lightweight metal studs and plasterboard?

I estimate that the wall will weigh about 1,000 kg if build out of AAC blocks (10 sq.m. at 8.33 blocks per sq.m. and approximately 9 kg per block, plus an extra 250 kg for supporting concrete columns and beams). My gut feeling tells me that spread out over 4 meters that is relatively light weight and should be able to be supported by the floor, but I really don't have any experience to back this up. Of course, if build out of metal studs and plasterboard, the wall will be much lighter.

I would prefer to build with the AAC blocks, since we already have those and my builder has experience building with them, but on the other hand I (obviously) don't want the floor to collapse. So, is anyone willing to give an opinion on whether the walls will be too heavy if built out of AAC blocks?

Thanks in advance.

Sophon

[menorah]

...... it should be possible to get some detailed load bearing information, relating to the concrete planks, from the supplier.

If that route fails then take a look at the info here: NB, you'll need auto translation operating for the 1st link but there are many others offering good online information

http://www.yongconcrete.co.th/priceListPFP.aspx

http://www.acp-concrete.co.uk/precast-concrete-products/floors-and-stairs/beam-and-block-floors/design-information/

For your information, I placed a 1000 Litre water tank on the roof of my 3 storey town house. It too wa was sitting across the join between two concrete planks and like you, I was a little anxious.

In my case the tank was only a short distance from the end of the planks and where they rested on the structural ring beam.

I did think the 1 metric tonne weight might possibly cause the concrete planks to distort..... but filled 'her up' anyway !

Two years on there's no indication of anything untoward and the entire area remains stable, free from cracks or movement.

If you're stlil worried, another option is to use the lightweight blocks but to incorporate strategically placed denser blocks where solid fixings are required. However, the strength of the finishing render coat, either face of the block work, generally provides a very strong fixing substrate.

Oh, I forgot to add...

usually prior to the concrete screed going down, either lengths of steel re-enforcing wires are attached over the planks or a wire grid / mesh.

You could easily have your builder weld together a much stronger area of re-enforcing steel mesh for placement along the joint and across the floor to further spread load.

It would cost very little to construct, approx' B500 and would disappear under the screed... 5cm and any subsequent ceramic tile layer and cement bonding 3cm.

[wayned]

If the beams/footings for the walls are not yet poured, I would move them to coincide with your new floor plan.. I know, easily said, but you most likely wouldn't be asking if they were already poured. Since it doesn't affect a bathroom wall I would use metal studs and wallboard rather than block.

[IMHO]

60x20x10cm AAC blocks end up 60kg/sqm before rendering.

60x20x7.5cm AAC blocks are 46.5kg/sqm.

Are you sure they only put down 5cm of CPAC on top of the planks? that seems very thin. We pour 10cm - which at 4M beam spacing can safely support 3000KG of distributed load - 5cm would be less than half of that - it's not linear.

[trogers]

Structural failure is not likely, but main problem with precast slab is excessive deflection of the slab creating problems for floor finishes, door and windows.

[bbradsby]

OP, your wall weight calc is incorrect. Assuming 10cm AAC block, the weight per m2 ( น้ำหนัก (กก.) ) of wall area is approx 7.5 kg/m2 plus finishes, nominal as long as you aren't facing the wall with stone or tile. Never mind the number of blocks or weight of each block. Then, remember to add the weight of any concrete bond beam (if any) at top of wall, plus any loads imposed on the top of wall, such as ceiling and/or roof framing.

Note that the AAC wall is pretty stiff and acts as a beam after the block adhesive sets up. The good news is, this benefits you by "spanning" from beam to beam so doesn't add to the bending stress on the precast floor slabs. The bad news is, it adds point loads on the aforementioned floor beams at both ends of wall. This is what should be looked at.

I assume the wall layout plan is your proposed/revised plan, while the beam plan is existing. Your drawings have all indications that they were drawn by an architect - ask him/her to advise…? Else, PM me and I can get my engineer to review and advise for a nominal sum so that you have peace of mind.

All the best,

[IMHO]

OP, your wall weight calc is incorrect. Assuming 10cm AAC block, the weight per m2 ( น้ำหนัก (กก.) ) of wall area is approx 7.5 kg/m2 plus finishes, nominal as long as you aren't facing the wall with stone or tile. Never mind the number of blocks or weight of each block. Then, remember to add the weight of any concrete bond beam (if any) at top of wall, plus any loads imposed on the top of wall, such as ceiling and/or roof framing.

Note that the AAC wall is pretty stiff and acts as a beam after the block adhesive sets up. The good news is, this benefits you by "spanning" from beam to beam so doesn't add to the bending stress on the precast floor slabs. The bad news is, it adds point loads on the aforementioned floor beams at both ends of wall. This is what should be looked at.

I assume the wall layout plan is your proposed/revised plan, while the beam plan is existing. Your drawings have all indications that they were drawn by an architect - ask him/her to advise…? Else, PM me and I can get my engineer to review and advise for a nominal sum so that you have peace of mind.

All the best,

I'm afraid it's your numbers that are wrong - 7.5kg per sqm *might* get you a gypsum wall with c-channel studs, but not AAC blocks

Refer to my earlier post for actual numbers from the manufacturer (60kg/sqm).

[thaibeachlovers]

If the beams/footings for the walls are not yet poured, I would move them to coincide with your new floor plan.. I know, easily said, but you most likely wouldn't be asking if they were already poured. Since it doesn't affect a bathroom wall I would use metal studs and wallboard rather than block.

That's certainly what I'd be doing.

[bbradsby]

OP, your wall weight calc is incorrect. Assuming 10cm AAC block, the weight per m2 ( น้ำหนัก (กก.) ) of wall area is approx 7.5 kg/m2 plus finishes, nominal as long as you aren't facing the wall with stone or tile.

I'm afraid it's your numbers that are wrong - 7.5kg per sqm *might* get you a gypsum wall with c-channel studs, but not AAC blocks

Refer to my earlier post for actual numbers from the manufacturer (60kg/sqm).

Right you are, and thanks for the correction. Was working off of their Thai site, and not careful enough… thats why I hire engineers! Here's qcon's English language site: http://www.qcononline.com/products/property_e2.php?id=e201

[Sophon]

Sorry for the delay in replying, but we have been quite busy with the house build the last couple of days.1

...... it should be possible to get some detailed load bearing information, relating to the concrete planks, from the supplier.

If that route fails then take a look at the info here: NB, you'll need auto translation operating for the 1st link but there are many others offering good online information

http://www.yongconcrete.co.th/priceListPFP.aspx

http://www.acp-concrete.co.uk/precast-concrete-products/floors-and-stairs/beam-and-block-floors/design-information/

For your information, I placed a 1000 Litre water tank on the roof of my 3 storey town house. It too wa was sitting across the join between two concrete planks and like you, I was a little anxious.

In my case the tank was only a short distance from the end of the planks and where they rested on the structural ring beam.

I did think the 1 metric tonne weight might possibly cause the concrete planks to distort..... but filled 'her up' anyway !

Two years on there's no indication of anything untoward and the entire area remains stable, free from cracks or movement.

If you're stlil worried, another option is to use the lightweight blocks but to incorporate strategically placed denser blocks where solid fixings are required. However, the strength of the finishing render coat, either face of the block work, generally provides a very strong fixing substrate.

Oh, I forgot to add...

usually prior to the concrete screed going down, either lengths of steel re-enforcing wires are attached over the planks or a wire grid / mesh.

You could easily have your builder weld together a much stronger area of re-enforcing steel mesh for placement along the joint and across the floor to further spread load.

It would cost very little to construct, approx' B500 and would disappear under the screed... 5cm and any subsequent ceramic tile layer and cement bonding 3cm.

The wall will not be close to the joint between two planks, but near the middle of one plank. So in effect the whole weight of the wall will be supported by one plank (plus the poured concrete).

Nothing will be fixed to the wall, other than the door, so no need for incorporating denser blocks. And I'm not worried about the walls where I will need to fix things, using the correct fittings even heavy things can safely be secured to AAC blocks.

With regards to your last suggestion, the floor was constructed several months ago, so too late to change it now.

If the beams/footings for the walls are not yet poured, I would move them to coincide with your new floor plan.. I know, easily said, but you most likely wouldn't be asking if they were already poured. Since it doesn't affect a bathroom wall I would use metal studs and wallboard rather than block.

As mentioned, columns, beams and floor was finished months ago so too late to do anything differently.

60x20x10cm AAC blocks end up 60kg/sqm before rendering.

60x20x7.5cm AAC blocks are 46.5kg/sqm.

Are you sure they only put down 5cm of CPAC on top of the planks? that seems very thin. We pour 10cm - which at 4M beam spacing can safely support 3000KG of distributed load - 5cm would be less than half of that - it's not linear.

The 9 kg per blocks was a guestimate, it seems that 8 is closer to the mark. Including plastering 9 kg is probably close enough to the truth.

yes, the plans calls for a 10 cm floor so that is what we have (consisting of 5 cm planks with 5 cm concrete on top).

Structural failure is not likely, but main problem with precast slab is excessive deflection of the slab creating problems for floor finishes, door and windows.

That would be serious enough.

I still think that building with AAC blocks would be OK, but with the potential (however slight) for problems, I think we will probably go with the metal/plasterboard wall (although, we will probably use Viva cement boards).

Thanks to all for their comments.

Sophon

[krisb]

Why can't you just get your builder to make the variation you want?

[Sophon]

Why can't you just get your builder to make the variation you want?

Sorry I don't understand what you mean. Of course I can get my builder to make what I want, that's why I'm trying to figure out here what I should tell them to do (what is safe).

Sophon