How to effectively seal a flat concrete roof?

[jvs]

6 hours ago, Dante99 said:

I think there are additives that should be mixed into the wet concrete that will help waterproof it.  Thais have been using such additives on bathroom floors particularly on upper levels for many years.  New products for this purpose have of course become available.  Check it out, probably can have concrete delivered with additive already mixed into it.

Yes,this is what we did on one project,also used for swimming pools.

[Encid]

2 minutes ago, Kwasaki said:

Does the architect know the builder. ? 

No. But our builder has heard of our architect.

 

2 minutes ago, Kwasaki said:

Have you seen any of the builders recent completed constructions.?

Yes - quite a few.

In fact he has just complete a build in Kalasin for another forum member, and he is very happy with the results. The builder suggested/pointed out a few better ways to do things than what the architect designed, and consequently saved him some money as well. He was very happy with the quality of the build and told me that he would definitely use this builder again.

 

5 minutes ago, Kwasaki said:

Keep an eye on what quantities of materials that are ordered.

A detailed BOQ is one of the deliverables from the architect, so it will form part of the contract with the builder.

Things like internal tiling and all the glazing I will probably supply myself, unless my builder can get the equivalent at the same or a better price.

[Kwasaki]

22 minutes ago, Encid said:

No. But our builder has heard of our architect.

 

Yes - quite a few.

In fact he has just complete a build in Kalasin for another forum member, and he is very happy with the results. The builder suggested/pointed out a few better ways to do things than what the architect designed, and consequently saved him some money as well. He was very happy with the quality of the build and told me that he would definitely use this builder again.

 

A detailed BOQ is one of the deliverables from the architect, so it will form part of the contract with the builder.

Things like internal tiling and all the glazing I will probably supply myself, unless my builder can get the equivalent at the same or a better price.

Good luck with you build hope all goes well. ????

[sometimewoodworker]

46 minutes ago, Encid said:

As it will be in direct sun only for a few hours in the early morning on the East side, and only for a few hours in the late afternoon on the West side, we are not anticipating a lot of thermal transmission.

 

Sure, there will be some... but it should be negligible (we hope).

The amount of transmission will undoubtedly be noticeable and probably not negligible. That is exactly why we installed the reflective blinds. The supervisor likes the warmth from the glass door and reflected heat from the blind, on the other area the other supervisor isn’t interested as she can’t easily get behind the blind

 

The late afternoon sun can only strike the windows for a small amount of time as the trees on the workshop side provide enough shade 

[sometimewoodworker]

27 minutes ago, Encid said:

Things like internal tiling and all the glazing I will probably supply myself, unless my builder can get the equivalent at the same or a better price.

Without question supply yourself, your builder has zero incentive to save you money, in fact saving you money probably costs him money.

[itsari]

The contemporary design you have chosen is pleasing to the eye , yet a flat roof is a far higher risk from problems .  Heavy rain can give problems if the outlets can not take the volume which can easily happen in Thailand .

[Muhendis]

A word of caution about the waterproofing of the roof.

You will need to be aware of how solar panels etc. are to be mounted so as to avoid damaging the waterproof bits.

It would be such a shame if any mounting holes went a tiny bit too deep.

I think I would personally go for the DPM and a minimum of 50mm RC if the roof is strong enough. 

[phetphet]

i know nothing about building, but isn't there something called waterproof concrete? Could you perhaps use that for the roof? Even if as a second skim.

[Encid]

15 minutes ago, Muhendis said:

A word of caution about the waterproofing of the roof.

You will need to be aware of how solar panels etc. are to be mounted so as to avoid damaging the waterproof bits.

It would be such a shame if any mounting holes went a tiny bit too deep.

I think I would personally go for the DPM and a minimum of 50mm RC if the roof is strong enough. 

Actually I was thinking that there will definitely be damage to the waterproofing coating when we install our future PV panels.

The architect was requested to design the roof sections to be capable of withstanding the load of full 450W arrays of PV panels (plus 100kg for maintenance personnel) and I can see from the drawings that he has applied an SF (safety factor) of 2.5, so the roof itself will be OK.

The panel supports will need to be secured against strong winds though, so the fixings will need to penetrate the coating and extend some 5-8cm (min) into the RC roof, as the sand mortar finish will not be strong enough by itself.

I was thinking along the lines of a tar-based product to seal around the panel supports after they have been installed.

[Encid]

2 hours ago, itsari said:

The contemporary design you have chosen is pleasing to the eye , yet a flat roof is a far higher risk from problems .  Heavy rain can give problems if the outlets can not take the volume which can easily happen in Thailand .

That is a very good point.

At the moment our 2" PVC outlets are spaced on average 5m apart.

That may be fine for the upper level and the interim level, but the lowest level will also be subject to the upper level runoff which will effectively double the volume of water it will have to handle.

If the drainage pipes cannot handle the volume of water it will simply flow over the sides of the roof and down the walls.

The external decking is 10cm below the concrete floor level inside the house (which is elevated 90cm above grade) so we will not experience any flooding inside, but it would obviously be preferable to collect and control the storm water runoff.

 

I will take a closer look at that thanks. 

[itsari]

1 minute ago, Encid said:

That is a very good point.

At the moment our 2" PVC outlets are spaced on average 5m apart.

That may be fine for the upper level and the interim level, but the lowest level will also be subject to the upper level runoff which will effectively double the volume of water it will have to handle.

If the drainage pipes cannot handle the volume of water it will simply flow over the sides of the roof and down the walls.

The external decking is 10cm below the concrete floor level inside the house (which is elevated 90cm above grade) so we will not experience any flooding inside, but it would obviously be preferable to collect and control the storm water runoff.

 

I will take a closer look at that thanks. i think you need 4 inch outlets minimum for  extra volume and ease of unblocking the down pipes 

 

[Elkski]

2" is to small and you will need to access all those different roof planes often to clean off leaves and sticks and clogged drains.   I don't see a leaf filter grate installed to keep small mammals from clogging the pipes?

So all these drain pipes will be ran to a couple of collection tanks?  Horizontal drain pipes need need a slope of like 1/36. 

Can't believe for 1 second you will get a 1/100 slope concrete pour without several pooling locations.   

What access is there going to be in the attic to find leak locations?  And what ceiling type and it's repairability will be used? It looks like there is a vertical wall extending above the flat roof. How will that joint be sealed? how about that vertical portion? There will be movement and cracking at those junctions!!!

What about the top of those walls?    

I say go with a welded membrane that goes up and over all the vertical walls and the walls are capped with a continuous metal cap with a drip edge to keep water from running down your exterior walls.   Solar installation is going to penetrate this nice membrane.  What does that do for their warranty?  

Looks nice but your going to have issues. 

Edited February 17, 2023 by Elkski

[Encid]

36 minutes ago, phetphet said:

i know nothing about building, but isn't there something called waterproof concrete? Could you perhaps use that for the roof? Even if as a second skim.

CPAC certainly does.

They can supply ready mixed "specialty" concrete.

 

From their website (via Google Translate):

"CPAC has researched and developed to have true waterproofing properties without having to add additional waterproofing agents at the job site and has high water opacity. It has been designed to meet the requirements of material and construction standards for concrete structure (Engineering Institute of Thailand) is therefore ideal for structures exposed to water, or humidity all the time, such as swimming pools, water tanks, bathroom floors, foundations, soil beams.

 

[Encid]

8 minutes ago, itsari said:

i think you need 4 inch outlets minimum for  extra volume and ease of unblocking the down pipes 

You might be right.

I will take a closer look at it thanks. 

[Elkski]

I just wanted to point out one more point of high probability of leaking.  Around each PVC drain pipe.  I assume that is a pipe that will just extent up pre- pour and be cut off flush later. First off cement slope and smoothness is hard to maintain around protrusions.   What schedule PVC pipe are the drains?The wall thickness of PVC  is less than 4mm.  So some painted on product will be able to adhere and seal to that small cross section?  Because if not then seepage will go down the pipe.  Are those pipes ran down in the hollow wall cavities? 

[Encid]

7 minutes ago, Elkski said:

2" is to small and you will need to access all those different roof planes often to clean off leaves and sticks and clogged drains.   I don't see a leaf filter grate installed to keep small mammals from clogging the pipes?

There are no trees anywhere near the house for hundred of metres so leaves and sticks and clogged drains will not occur.

No leaf grates are required as there are no leaves.

And we plan to keep it that way.

 

Small mammals?

We are building in Isaan.

People eat small mammals there... 

 

11 minutes ago, Elkski said:

So all these drain pipes will be ran to a couple of collection tanks?

Most will be dumped into our pond behind the house which is currently being used to raise tilapia (fish).

That overflows into the farm which is currently being used to grow rice.

But I'd like the option to divert some of the water (clean) to supplement our water storage tanks for domestic use (after filtration).

 

16 minutes ago, Elkski said:

What access is there going to be in the attic to find leak locations?

Attic?

What attic?

There is no attic.

 

17 minutes ago, Elkski said:

And what ceiling type and it's repairability will be used?

As is usual in Thailand the ceiling will be a suspended gyprock or smartboard ceiling (Google "SCG smartboard").

It will be covered with 150mm thick SCG STAYCOOL insulation so leaks (if any) will not be easy to locate.

If the roof leaks somewhere then we won't know about it until the ceiling discolours from water damage and maybe drips to the floor below.

Not an easy job to repair hence the questions/discussion on effective sealing methods.

 

25 minutes ago, Elkski said:

Solar installation is going to penetrate this nice membrane.  What does that do for their warranty? 

This is Thailand, not the USA.

Builders do not warranty their builds here (on average - a few will, but those companies and their builds come at a premium price).

 

[Kwasaki]

35 minutes ago, Encid said:

That is a very good point.

At the moment our 2" PVC outlets are spaced on average 5m apart.

That may be fine for the upper level and the interim level, but the lowest level will also be subject to the upper level runoff which will effectively double the volume of water it will have to handle.

If the drainage pipes cannot handle the volume of water it will simply flow over the sides of the roof and down the walls.

The external decking is 10cm below the concrete floor level inside the house (which is elevated 90cm above grade) so we will not experience any flooding inside, but it would obviously be preferable to collect and control the storm water runoff.

 

I will take a closer look at that thanks. 

Weir flows can be Installedd in such  downpour situations.

[Encid]

14 minutes ago, Elkski said:

I just wanted to point out one more point of high probability of leaking.  Around each PVC drain pipe.  I assume that is a pipe that will just extent up pre- pour and be cut off flush later. First off cement slope and smoothness is hard to maintain around protrusions.   What schedule PVC pipe are the drains?The wall thickness of PVC  is less than 4mm.  So some painted on product will be able to adhere and seal to that small cross section?  Because if not then seepage will go down the pipe.  Are those pipes ran down in the hollow wall cavities? 

Typically roof drainage pipes which pass through concrete (before pouring) are fitted with a "puddle flange" which can be drilled and wired in position to the nearby reinforcing steel before being encased in concrete.

The schedule or wall thickness of the PVC pipe is irrelevant as it is not pressure retaining.

Seepage will not run down the pipe because the puddle flange will stop it. And so what if it does? It's only going to drip onto the lower level.

No, the down pipes will not be run down the inside of the cavity walls... that is reserved for electrical conduits and water supply and vent piping.

[Elkski]

I would consider the space between ceiling and drop tiles as an attic.  And yes mold Will occur before you know about the leaks.   A flage with a broad area for the membrane to adhere to is what I was hoping for.  I saw the cup depression in that detail drawing but didn't know how that was made.  It looked like it was only in the sand slurry .    

You still didn't address the cracking and movements that will occur between the roof slab and vertical walls or the side and tops of those walls.  Welded

Membrane companies don't have a warranty in Thailand? They also have ways to pre install and waterproof equipment mounting support points.  

So somehow the upper roof drains exit out into the lower roofs?  How do those lower roofs drain to the pond?   

Wind can blow leaves and debris a long ways.  Can't believe in 30 years you won't have any plants nearby.  How easy will it be to ladder up to all the levels?  

[jvs]

1 hour ago, Encid said:

Actually I was thinking that there will definitely be damage to the waterproofing coating when we install our future PV panels.

The architect was requested to design the roof sections to be capable of withstanding the load of full 450W arrays of PV panels (plus 100kg for maintenance personnel) and I can see from the drawings that he has applied an SF (safety factor) of 2.5, so the roof itself will be OK.

The panel supports will need to be secured against strong winds though, so the fixings will need to penetrate the coating and extend some 5-8cm (min) into the RC roof, as the sand mortar finish will not be strong enough by itself.

I was thinking along the lines of a tar-based product to seal around the panel supports after they have been installed.

If you pre plan you can already pour anchors when you pour the roof,

That way they will never leak and are a lot stronger.

Pieces of ready rod sticking out far enough leaves a lot of options.

 

[Kwasaki]

9 minutes ago, Elkski said:

I would consider the space between ceiling and drop tiles as an attic.  And yes mold Will occur before you know about the leaks.   A flage with a broad area for the membrane to adhere to is what I was hoping for.  I saw the cup depression in that detail drawing but didn't know how that was made.  It looked like it was only in the sand slurry .    

You still didn't address the cracking and movements that will occur between the roof slab and vertical walls or the side and tops of those walls.  Welded

Membrane companies don't have a warranty in Thailand? They also have ways to pre install and waterproof equipment mounting support points.  

So somehow the upper roof drains exit out into the lower roofs?  How do those lower roofs drain to the pond?   

Wind can blow leaves and debris a long ways.  Can't believe in 30 years you won't have any plants nearby.  How easy will it be to ladder up to all the levels?  

No house is maintenance free your going a bit OTT. 

[unheard]

16 hours ago, jvs said:

If you pre plan you can already pour anchors when you pour the roof,

That way they will never leak and are a lot stronger.

Pieces of ready rod sticking out far enough leaves a lot of options.

 

That would require communication between the architect and the solar company - the solar install would need to be finalized and then translated into the houses' roof plan well before construction starts.

Not as simple as it sounds.

[d4dang]

22 hours ago, Encid said:

The walls are designed as cavity walls with 7.5cm AAC blocks on the inside and outside with a 5cm air gap between.

Both inside and outside will be rendered and painted with appropriate paint to ensure they are waterproof.

 

If you looked at the images I posted before you will see that the entire house is raised off the ground... by 90cm actually.

The external decking will be 80cm above grade level... just like the Thais have been doing for centuries.

And the whole building site has also been raised some 1.8-2m above the highest recorded flood level in the province.

 

But none of this has anything to do with sealing a flat concrete roof...

Could you give us an estimate of the cost of your new home? Looks great. I doubt I could afford it. Is it a rural lot or ocean side or?

[Kwasaki]

31 minutes ago, unheard said:

That would require communication between the architect and the solar company - the solar install would need to be finalized and then translated into the houses' roof plan well before construction starts.

Not as simple as it sounds.

Don't put the solar panels on the roof the ground is not that much further from the sun. ????

[Encid]

3 hours ago, d4dang said:

Could you give us an estimate of the cost of your new home? Looks great. I doubt I could afford it. Is it a rural lot or ocean side or?

It is going to be built in rural Isaan on a small farm about 2km from the nearest village, so despite having a small government road to access the property, there are no government services (water, power, internet) available.

 

The internal living area is 168 sq.m.

The external Thai Kitchen and the Utility/Battery room in the garage is another 35 sq.m.

The external decking area is 84 sq.m.

The carport is another 70 sq.m.

Total footprint size is 357 sq.m.

 

The basic house cost estimate (depending on quality of fitout materials) and including the pool and accessories is around 6 million baht.

[Encid]

2 hours ago, Kwasaki said:

Don't put the solar panels on the roof the ground is not that much further from the sun. ????

That is Plan B... and I am already looking into that option too. 

[d4dang]

10 hours ago, Encid said:

It is going to be built in rural Isaan on a small farm about 2km from the nearest village, so despite having a small government road to access the property, there are no government services (water, power, internet) available.

 

The internal living area is 168 sq.m.

The external Thai Kitchen and the Utility/Battery room in the garage is another 35 sq.m.

The external decking area is 84 sq.m.

The carport is another 70 sq.m.

Total footprint size is 357 sq.m.

 

The basic house cost estimate (depending on quality of fitout materials) and including the pool and accessories is around 6 million baht.

WoW....sounds great....maybe one day I will drive by and see it. Enjoy your dream home. Most of my 30 plus here was in shoe box apts....

[d4dang]

10 hours ago, Encid said:

That is Plan B... and I am already looking into that option too. 

I have an Ozzie friend who did solars for yonks...he is here in Th if you need advice

[Mark Nothing]

I volunteered on two condo boards over the years and we unsuccessfully dealt with flat roof leaking problems using a multitude of remedies similar to your ideas, none of which worked.

 

The penthouse owners were constantly complaining about leaks and black ceilings.  Year after year we tried different solutions at big expense.  

 

Pooling occurred on the flat roof after each rain and concrete cracks developed and grew over the years.  During heavy rain season the water drain pipes were too small to handle the volume of water to drain down, which caused backup of water and the roof flooded and the water entered condos.

 

Your house design is very nice though.

 

 

[HighPriority]

16 hours ago, Encid said:

That is Plan B... and I am already looking into that option too. 

I’m pretty unsure of the rooftop solar myself, waterproof membranes work best like an old fashioned swimming pool liner… Anything that penetrates that membrane increases the likelihood of leakage.

Ground based solar has its own issues, but I’d personally lean that way in this situation.