Designing for blown beads at the cavity bottom.

[epsilonGreedy]

I am about to start the construction of my footing blockwork and I want to ensure blown beads remain an option for cavity insulation later in the build.

 

Do I need to build in a tray to prevent beads settling at the bottom of the cavity below ground ground level?

 

I am in rainfall zone 1 / 2.

 

 

[Declan52]

The beads won't be sitting at the very bottom though. By the time both walls are built the droppings of motar will have filled up an inch or two. As they are EPs type beads it won't matter anyway if they are submerged in water. 

If you're cavity is constantly filling with rain then  something major has gone tits up.

[epsilonGreedy]

16 minutes ago, Declan52 said:

The beads won't be sitting at the very bottom though. By the time both walls are built the droppings of motar will have filled up an inch or two. As they are EPs type beads it won't matter anyway if they are submerged in water. 

 

 

Thanks. I am less troubled by the thought of soggy insulation beads at the bottom of a cavity than than cavity batts. The regs for cavity cement fill in footings and the newer requirement for such batts to insulate the edge of a block floor results in little clearance.

 

The pro insulation beads material online claims that batts are more likely to wick moisture than beads.

[Jeremy Harris]

3 minutes ago, epsilonGreedy said:

The pro insulation beads material online claims that batts are more likely to wick moisture than beads.

 

 

I'd go with that.  I had a plastic bag full of blown bonded beads that I filled when the guys were putting in our CWI.  I split the bag into two more or less equal lumps, let the glue dry for a few days, weighed each lump, then immersed one of the lumps in a bucket of water, weighed down by a brick, for a few days.  When I took it out and checked the weight it was near enough exactly the same as when it went in.  On the basis of one, impromptu and uncontrolled, experiment, I'd conclude that blown bonded beads don't absorb water at all to any significant degree.

[Declan52]

My cavity insulation went approx 300mm below my finished floor so there would be no cold spots. As you are going for a brick finish you could build in some weep vents level where you bring the concrete in the cavity up to. Then if any moisture gets that far it can seep out.

https://www.wickes.co.uk/Wickes-Wall-Weep-Vent---10-x-65mm/p/224684

[epsilonGreedy]

15 minutes ago, JSHarris said:

I had a plastic bag full of blown bonded beads that I filled when the guys were putting in our CWI.  I split the bag into two more or less equal lumps, let the glue dry for a few days, weighed each lump, then immersed one of the lumps in a bucket of water, weighed down by a brick, for a few days.  When I took it out and checked the weight it was near enough exactly the same as when it went in.

 

 

You are a one-man national research institute into house building, the Government should fund you.

 

17 minutes ago, JSHarris said:

On the basis of one, impromptu and uncontrolled, experiment, I'd conclude that blown bonded beads don't absorb water at all to any significant degree.

 

 

That is high science to me.

[Jeremy Harris]

9 minutes ago, epsilonGreedy said:

 

You are a one-man national research institute into house building, the Government should fund you.

 

 

That is high science to me.

 

 

I'm far from alone - @SteamyTea does just as many experiments to prove or disprove things.  If I can't find any hard evidence to prove something I find questionable, the chances are I'll do a quick experiment to better understand it. 

 

I still have to dig out the two bits of PIR foam that have been sat outside with lumps of mortar on for months and see if the mortar has had any effect at all on the foil coating.  Might dig them out next week and see how they look.

[PeterW]

I did just this fill however :

 

- below ground is 100mm EPS with a 25-45mm 6:1 sand cement fill in the remaining cavity. 

- there is a second DPM cavity tray up the inside of the first block lapped down and across to the outer DPM

- all cavities were cleaned (and hoovered....) before the closers installed and beads blown in. 

 

[epsilonGreedy]

24 minutes ago, Declan52 said:

My cavity insulation went approx 300mm below my finished floor so there would be no cold spots. As you are going for a brick finish you could build in some weep vents level where you bring the concrete in the cavity up to. Then if any moisture gets that far it can seep out.

 

 

I did wonder if water arriving at the bottom of a cavity would seep through a lean mix cement fill. Yes proper weep vents are to be included just not sure at the moment how to interpret NHBC advice on how high they should be. 

[epsilonGreedy]

4 minutes ago, PeterW said:

- there is a second DPM cavity tray up the inside of the first block lapped down and across to the outer DPM

- all cavities were cleaned (and hoovered....) before the closers installed and beads blown in.

 

 

I am not sure I have enough openings to allow such a cavity tray clean up.

 

My building control diagram depicts a similar upper dpm tray as shown in your photo though this could promote creation of a moisture bridge, I am sitting on the fence re. this choice.. 

[PeterW]

Unlikely - how do you plan to get moisture into the cavity other then when it’s being built...??

[epsilonGreedy]

8 hours ago, PeterW said:

Unlikely - how do you plan to get moisture into the cavity other then when it’s being built...??

 

 

It is an unavoidable consequence of wind driven rain seeping through the facing brick skin apparently.

[PeterW]

I’ve never seen it in nearly 30 years. To soak through 4” of brick at any rate to cause water in the cavity would need some serious hydraulic pressure. If it was an issue then full fill cavity insulation wouldn’t be allowed. 

[Brickie]

16 hours ago, epsilonGreedy said:

am not sure I have enough openings to allow such a cavity tray clean up.

That’s what coring holes are for. 

Leave out every 4th brick on Dpc & loop some hessian from one coring hole to the next. Every morning,you simply turn the hessian loop,bringing any mortar droppings from inside the cavity to the outside. Anywhere you have a door opening can be cleaned with a batten,rodding any droppings to your coring holes but you need to take care not to get too vigorous & make a tear in the tray. 

[epsilonGreedy]

10 hours ago, PeterW said:

I’ve never seen it in nearly 30 years.

 

 

Well that is very odd since it is a universally recognized factor in any debate over full fill cavity insulation, why do building regulations recognize rainfall zones when full fill cavity insulation is being discussed.

 

Anyhow mortar joints are the weakness.

Edited July 22, 2018 by epsilonGreedy

[PeterW]

2 hours ago, epsilonGreedy said:

 

Well that is very odd since it is a universally recognized factor in any debate over full fill cavity insulation, why do building regulations recognize rainfall zones when full fill cavity insulation is being discussed.

 

Anyhow mortar joints are the weakness.

 

Unless you’re planning on moving your entire house to a severe rated zone, why are you even bothering to debate this ..?

 

The building industry has been full filling with bead for over 25 years and I’ve not heard of an issue - it’s also very common in Ireland (as @Declan52 was referring) and they get a lot more rain than the rest of the UK. 

 

If you’ve already submitted - and have had accepted - your BRegs plans then what’s the issue building to these ..?? Be careful making amendments as you may be made to change the work at a later date 

[Declan52]

I think your worrying about nothing. Unless your house can get hit by a tidal wave the volume of water that will fully penetrate bricks or rendered blocks is minute.

As @PeterW says this type of cavity fill had been used on refurbs here for ages but only really took off for new builds on the last 10-15 years. That was primarily due to poor workmanship from brickies where large gaps would have got left in behind the cavity boards we use here. No site in 20 years that I have been on has used the Rockwool type batts that are used in the rest of the UK.

The beads aren't loose like they used to be. Once blown in at high pressure and the glue sets they form a solid block that no moisture can penetrate. Any moisture will fall down against the bricks and evaporate out your weep vents. 

If your brickies can't get the motar to stick on the bricks to form good perps then you have got chancers with tools not brickies. 

[epsilonGreedy]

19 hours ago, PeterW said:

Unless you’re planning on moving your entire house to a severe rated zone, why are you even bothering to debate this ..?

 

 

A common complaint in this forum is about mainstream building subcontractors making mistakes and taking shortcuts. I am flummoxed as why I should be castigated for seeking clarification on the finer point re. where cavity fill insulation should stop.

 

This is obviously a general industry concern and is a subject of evolving official standards. 10 - 20 years ago it was accepted that cavity batts should stop at DPC, now today in pursuit of better insulation the experts have decided to trade positioning insulation lower in the cavity for lower heat loss.

Edited July 23, 2018 by epsilonGreedy

[epsilonGreedy]

18 hours ago, Declan52 said:

The beads aren't loose like they used to be. Once blown in at high pressure and the glue sets they form a solid block that no moisture can penetrate. Any moisture will fall down against the bricks and evaporate out your weep vents.

 

 

Point of order. The promotional material publish by the pro cavity bead industry actually states that the glued bead lattice is permeable to water. Unlike batts the bead lattice is self draining, this is a positive apparently.

[Ian]

@epsilonGreedy

During renovation and rebuilding works where the inner leaf of the cavity wall has been taken down I've seen water running down the inner 'cavity' side face of the outer brick wall. On several occasions the outer walls were so badly built that you could read a newspaper through them. The weakness was unfilled or partially filled vertical perpend joints in the brick.

 

BTW - here's the English Building Regs Approved Doc diagrams regarding this issue of full fill of cavities.

 

Edited July 23, 2018 by Ian

[joe90]

Well, we did similar to PeterW , eps below DPC but rockwall batts above DPC, full fill. They have a BBA cert for this, even in our area (north Devon coast). Yes we have weep vents at DPC and window tray levels In case any moisture does get into the cavity. All working fine. The batts were installed as the walls rose so any snots were removed from the insulation as the next layer was installed. Our builder has built many houses the same way and he has never been called back to a job.

[epsilonGreedy]

18 minutes ago, joe90 said:

The batts were installed as the walls rose so any snots were removed from the insulation as the next layer was installed. Our builder has built many houses the same way and he has never been called back to a job.

 

 

When discussing batts v. beads with a brickie team they claimed batts were better because mortar drops were caught as you mention. In contrast they claimed with an end of build bead fill there was nothing to stop mortar drops building up on cavity ties below.

 

When sounding out my building adviser about this process he wrinked his nose in disapproval and said using batts to catch mortar drops works fine during good weather but on other days dropped mortar can squelch down into the batt fibre and create a moisture conducting matt. My adviser said he would loan me his custom mortar catch traps that are moved upwards daily as the inner blockwork catches up with the facing brick height.

 

I don't know who to believe any more, the building trade seems to operate on bravado, superstition and witchcraft.

 

Right now I feel like following my own intuition providing it does not transgress building regs.

 

I will:

1. Fit blown bead insulation at the end of the build in warm dry mid summer conditions to ensure good circulation of the beads in the absence of cavity moisture.
2. The above ground dpc will be implemented as two independent courses and thus beads will settle low in the cavity to provide anti cold bridge insulation to the beam & beam of the suspended floor.
3. The inner wall dpc will be lapped with the above block floor membrane.
4. Thin-joint inner blockwork will reduce total wall mortar usage by 14% and so reduce the chance of wall-tie mortar bridges.

[joe90]

Quote “ there is no such thing as right and wrong there is only opinion”.

[Declan52]

3 hours ago, epsilonGreedy said:

 

Point of order. The promotional material publish by the pro cavity bead industry actually states that the glued bead lattice is permeable to water. Unlike batts the bead lattice is self draining, this is a positive apparently.

There is a difference though in the fully glued up beads being permeable to water and stopping water from the outside penetrating through the cavity till it gets to your inside skin.

Being beads they will have tiny air gaps when they form the solid mass in your cavity. Any moisture  that gets through will drip down from bead to bead through the air gaps till it either goes out through the bricks through evaporation or falls all the way down to the bottom of your cavity and makes its way out through your weep vents. Either way none should travel across the cavity.

This is assuming that your wall ties are built in correctly which I have seen wrong on many occasions.

@Ian examples where caused by poor workmanship where the brickies never put enough motar on the edge of the brick to form good perps. If the guys you have chosen to build your house can't do this then you need to tell them to pack up their tools and leave.

[WWilts]

On 23/07/2018 at 11:07, epsilonGreedy said:

custom mortar catch traps

Pls say how these can be made/used?

Plenty of mortar droppings happening daily. Worried that
a) the weepholes will be blocked up

b) the insulation will not extend low enough in the cavity (bonded EPS beads blown in)

And how does one clean out mortar droppings, now that every 4th brick has not been omitted at the base (Brickie's brilliant idea)? Can one knock out bricks from the base of a wall that is already over 1.8m high?

PS At right, note also the external leaf of the doorway. DPC turned up rather than down. What will that do to any rain that bounces up above the second DPC? Or is the >150mm height of that enough to allay any concerns about bouncing rain?
 

Edited October 14, 2021 by WWilts
found a solution for mortar board