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Full filling of Masonry Cavity wall construction with polystyrene blown in insulation beads. YAY or NAY?

Hey guys, basically I'm just looking for any opinions on the subject of insulating masonry homes in terms of moisture build up and structural issues (outer and inner leaf of concrete blockwork, with a cavity between, of at least 100mm (4") gap and exterior face usually stuccoed or pebble dashed over this).

Here in Ireland, a popular way over the last few years to retrofit homes built of concrete cavity wall construction as mentioned above (built from 1970's onwards) is to insulate between the concrete leafs fully with blown in, bonded EPS beads. I have read some of the articles on this site regarding insulating of the interior side of old solid multi-whyte brick buildings particularly in the northeast of the US in urban areas resulting in structural concerns and moisture damage to the brick facades due to the prevention of drying on the interior by the new insulation.

Is there a similar concern that by fully insulating the cavity space in block cavity wall homes, this may damage the exterior leaf as it cannot now dry on its interior side? Is this concern less valid when talking of block exterior facades of only 4" thickness? Is it only of real concern when it is load-bearing like the inner leaf for example, and not much of an issue on the exterior? Many homes actually have a brick exterior, cavity space then a concrete block inner leaf; are these brick facades more of a concern when filling the cavities than a concrete block exterior leaf? Climate is wet, windy and generally somewhere between mild and cold.

These bonded EPS beads are supposed to allow moisture ingress from the exterior leaf to trickle downwards along the waxy surface of the beads preventing moisture build up or ability to travel inwards but I don't see anyone speaking about ventilation to actually DRY the cavity face of the brick/blockwork exterior leaf? Any opinions out there?

Asked by Tim O Brien
Posted Jan 20, 2012 9:27 PM ET
Edited Jan 20, 2012 9:29 PM ET


3 Answers

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You're asking the right questions. I don't have enough experience with Irish construction techniques to provide an answer.

In the U.S., brick veneer homes usually have wood-framed bearing walls. In such homes, the air gap between the brick veneer and the wall sheathing is an important element of the wall, and this gap shouldn't be filled with insulation.

When the inner wall consists of concrete block construction, there is obviously less of a concern about mold and rot. But it's still conceivable that by insulating the cavity, moisture will be transferred more readily to the inner wall.

Your question should be directed to an Irish building scientist. Does your country have any of those? Is any academic or research facility building wall mock-ups and testing them?

Answered by Martin Holladay
Posted Jan 21, 2012 6:59 AM ET


Full-fill cavity insulation techniques in various forms have been around in the UK and presumably Eire also for many years, and I recall from my days of practicing there in the 1980's that there were frequent failures. As both wythes of a masonry cavity wall are porous and as wind-driven rain in these climates will often thoroughly soak the exterior component of the wall, the issue is not whether the interior face of the exterior wythe is able to dry but rather does the cavity fill allow water to jump the cavity and wet the interior wall*. Seems like the 'waxy surface' of the bonded EPS beads you describe is intended to mitigate this effect and preserve the rainscreen drainage plane that the careful flashings of a properly constructed cavity wall are designed to maintain but I wouldn't bet the family farm on it. The manufacturer should be able to refer you to performance testing information but until the technique has been around for a good few years and has a long-term clean bill of health, call me conservative but I'd avoid competing for the 'first-in-block, OMG what have I done to my home' award.

* Here the concern is not structural failure of the wall due to rot, as it would be in wood-frame construction. But black mold growing up the peeling wallpaper is not nice to live with and not good for resale value.

Answered by James Morgan
Posted Jan 21, 2012 9:21 AM ET


Thanks Martin and James for that,
Martin, research into extensive interior insulating of masonry constructions is ongoing lets say! I know of late, research has been done in a harsher climate such as Scotland and they too have concerns about this topic. Research on traditional methods is minimal here up to recently. Masonry buildings were built to be solid, breathable and last and so nobody worried any further. Only since large amounts of insulating has become a norm has this problem cropped up with moisture analysis. When the interior block leaf was insulated internally there was no problem but as of late full filling the cavity has become the norm, particularly since people don't want to lose more space on the interior side, and this is what possibly concerns me, bridging that cavity.

James, I didnt realise they fully filled cavities that far back! Outside of experimental methods I think filling the remainder of a cavity with insulation beads is only popular as a retrofit measure here in Eire over the past 10 years or so. Before that, cavity walls were built partly insulated in the cavity with rigid foam insulation using EPS quite often, as much of the UK has done too I presume. (100mm cavity with 50 to 75mm (2 to 3") insulation)
The beads are intended to do as you describe but like you I would be very cautious about betting on there effectiveness against moisture travel until they have been around longer. (Cowboy story Number 1 coming up)

A botched job with fitting a simple extract ventilation pipe from a ground floor inner bathroom, to the exterior wall meant that not only was the vent pipe not properly attached to the grill in the wall but the grill was permanently cemented into that wall and not so easily taken off to replace or see whats going on inside.....This leads to the problem...Our cavities filled with EPS beads. When the weather cools and hits the winter time the temperature and pressure differences causes the beads to get sucked into the extract pipe from the cavity wall in the vicinty of the exterior grill, and fall into our bathroom through the fan unit in the ceiling, usually happens for a couple of days and then whenever we experience very windy weather with temperature swings it can happen there aswell....Them beads dont appear to be stuck together as advertised either....not only did they come out through the fan but they came out under the base boards along the north eastern side of the house aswell ....they came out in a few places where air currents pushes them out....quite annoying....not so much anymore since I had to seal the gaps along the boards and the floor with clear silicone which did work thankfully, for now. SO be careful next time an installer suggests blowing your walls with beads that are supposed to bond together!!

Answered by Tim O Brien
Posted Jan 21, 2012 10:38 PM ET

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