Don’t Fall Foul of Full Fill
It is almost a foregone conclusion that in order to meet the latest Part L and SAPs, separating wall cavities will need to be fully-insulated to give the required zero U-value.
In robustdetails®, there are two ways to achieve this:
> built-in roll or batt insulation that is installed as the wall is being constructed;
> blown-in insulation that is installed after the wall blockwork is completed
But both are dependent on the cleanliness of the cavities, which can very quickly have an effect on the acoustic standards – especially in blown installations.
Built-in insulation has the advantage of allowing mortar and debris to be cleared from the cavity in stages as the wall is built (usually every 2 courses): blown insulation on the other hand, gives the opportunity for debris to build up from the whole height of the separating wall.
There are a number of very good reasons why a builder would want to use blown insulation – but as our monitoring has highlighted, we are also seeing it reducing standards… so construction of these wall types requires an even greater focus on workmanship.
Built-in Clarity
Rolls of insulation, typically used for the built-in option, are 450mm wide to fit between the rows of wall ties, so as we can see in this work in progress, any mortar droppings can (and should) be cleared from the insulation that’s installed before the next layer is rolled out and second leaf built up.
Without proper care, it is possible to get quite a decent collection of mortar even from a couple of courses of blockwork… as witnessed here as the wall extended up into the roof space.
The bridging caused by this type of mortar accumulation, especially in the roof space, is unlikely to cause a significant reduction in performance by itself – but if there are excessive amounts on every insulation layer; and especially when combined with other detrimental factors, such as having an increased number of wall ties around movement joints, then the cumulative effect could be sufficient to result in a test fail.
Blown mind
When using blown insulation, there is not the same visibility due to the whole height of the wall being constructed before any insulation is installed; so it is vitally important to mind that excessive amounts of mortar don’t disappear down the cavity – not only to accumulate at the base, but also to build up on the wall ties.
This is particularly important where a gas membrane or other DPC / DPM is continuous across the cavity, as the accumulation of mortar will now bridge the cavity where the wall separates one room from another. This in itself could be enough to cause a test fail.
Ideally, sites will have controls in place that minimise mortar in the cavity in the first place, such as using draw-boards or sections of gutter in the cavities, but if these controls aren’t there, then other measures need to be taken.
One way to deal with this aftermath is to leave intermittent blocks out at the base of the wall, so the cavity can be cleared and blocks replaced. However, if this is left right until the end, the mortar deposits could have solidified and be very difficult to remove.
Alternatively, the Icopal-MONARFLOOR® BRIDGESTOP® System can be included. Use of this system is shown in Appendix A2 to the robustdetails® Handbook.
Although this won’t prevent mortar from dropping into the cavity, the quilt that is applied to one leaf means the mortar droppings only make contact with one leaf, which effectively then stops the bridging effect across the cavity.
Summing Up the Filling Up
To avoid sound issues, whichever insulating method is used, the cavity must not be bridged by mortar droppings and other debris.
> If an insulation product is named in the chosen wall, that insulation product must be used;
> Injection holes should be properly back-filled with mortar, not just smeared over.