Internal Dry Lining - sense check and recommendations - Sth Dublin

edanto

I've been reading up about the various insulation options and I think that I'm going to go for Internal Dry Lining.

The house is a 40 year old semi-D.

Only one of the radiators in the house is on an external wall, so that's the only one to be moved. It's in the upstairs bathroom, which will have fairly big renovations anyway (moving bath&shower/retiling etc). Another plus of Internal for me is that I'll be putting in a bunch of extra cables and Internal will allow me to hide them more easily.

Nothing in the kitchen is on an external wall, so no extra work there. The whole place needs redecoration anyways.

I haven't gotten many quotes yet, and would be grateful for recommendations of firms from the approved list. Particulary from people that have had good work done by any one particular firm.

My main reason for not going for External is cashflow. Trying to keep the price as low as possible, and achieve better insulation.

Are there other big things that I should consider in the External/Internal decision?
thx

sinnerboy

Can't recommend any particular contractor - anyone who can should do so pm only please.

The most important thing to be aware of with dry lining is the risk of interstitial condensation (IC) that is condensation forming on the internal wall face behind the new insulation. Any wallpaper must be removed and if their is any existing plasterboard on dabs - this must also be removed. If either are left in place you will get mould growing.

Also if you overdo the insulation you increase the risk and duration period of IC formation. Aim for a U Value no better than 0.5 W/m2K . Now this will cause you problems if you are seeking Grant aid from SEAI who don't appear to be aware of basic building physics in requiring a U value of 0.27 W/m2K when processing Grants.

Remember to leave timber grounds ( battens ) to all locations you may need good fixings - over windows for curtains for example.

sinnerboy

Also - take the opportunity to improve air tightness by installing air tight tape between your window frames and the bare block walls before you dry line.

edanto

Thanks, that's very helpful advice.

I think my external walls are plastered directly (as opposed to board on dabs), and if so, that plaster stays on the walls before they get insulated, right?

Interesting what you say about the U-value, I'll have to understand that a bit more before I go ahead. So, SEAI grant requires you to get a u-value that is lower than your recommendation of .5 W/m2K. Will the SEAI refuse to pay a grant if I get a job done to the .5 U? Where does that value of .5 come from? Is there a work around in practise?

I'll look into battens as well, thanks.

sinnerboy

edanto wrote: »

Where does that value of .5 come from?

Figure 8 of this which shows cases of insulated plasterboard . Other options are tabulated too but note what happens in every case over time when one over insulates - the wall gets wetter and wetter.

Wet plaster ( meaning trowelled on ) can stay.

SEAI will not pay if you insulate to less than 0.27 W/m2 i.e. if you insulate to 0.5 W/m2K . I have no answer to this problem.

Go SEAI !

edanto

Very interesting article you linked to. Not finished reading it yet, must travel home. But at one point, he quotes from another book saying "when driving rain and rising damp are dealt with then - and only then - is interior insulation better than no insulation"

His model was based on as assumption that 70% of driving rain is absorbed by the external wall - to me that seems far higher than I would have expected, but of course I'm an absolute beginner.

I'm just amazed that my pebble dash walls would be absorbing so much water when it's raining. If it's as important as he says, I'd want to know a great deal more before I decide what to do.

Am I getting distracted by a red herring?


EDIT:

Another extract:

josephlittlearchitects.com wrote:

One striking conclusion of this comparative series of simulations is that higher and higher levels of external insulation appear to create healthy and ever more stable conditions within the wall buildup, while even relatively modest levels of internal insulation face tougher conditions and either failure or are bordering on doing so. An equally significant conclusion is that the right treatment of the external face appears to allow the installation of internal insulation without risk of growth in internal moisture levels.

BryanF

I agree with sinnerboy & J.little re drylining issues
have you done your sums on this: we know EWI is more expensive but what is the real difference considering labour and materials to dry-line all external walls + painting and redecoration of all rooms following the work?

if you do go for DL why not install a couple of humidity sensors between the dry-lining and the wall, they cost circa 50€ each, this way you can tell if conditions are occurring that would lead to dampness/mould.

I've also seem conservation 'specifiers' & 'specialists' install vents at the top and bottom of the plaster board to allow some ventilation to take place in the insulation space... I'm very sceptical about this, but it is still common practice!

edanto

Haven't yet done all of the sums, in the process of gathering quotes. Initial quotes for external are coming in at around double the internal price.

That includes associated works. Redecorating is moot, since the whole place needs to be redecorated anyways, we'll be doing it whether we insulate internally or externally. Also, only one rad on an external wall, so minimal plumbing cost (bathroom & sink).

I have an open mind 'til I decide completely - still gathering costs at this stage, but looking like internal is better for our particular house & budget (more so the budget).

sinnerboy

edanto wrote: »

His model was based on as assumption that 70% of driving rain is absorbed by the external wall - to me that seems far higher than I would have expected, but of course I'm an absolute beginner.

No your wrong and then right - this extract is from the software manual used by the writer r.r.f = rain reduction factor

The r.r.f. takes into account that some of the rain water hitting an inclined surface splashes off on impact and is therefore not available for capillary suction.

WUFI calculates the rain load on the component from the data in the climate file and multiplies it by the r.r.f. The resulting rain quantity is offered to the component for capillary suction. (The component may imbibe the offered quantity or less, but not more).

The r.r.f. depends on the roughness, orientation and inclination of the surface, and on the nature of the precipitation (rain, snow...).

With horizontal surfaces, the r.r.f. is usually one, since the scattered drops fall back to the surface.

With vertical surfaces, it is nearly zero for snow and hail, for other conditions it must be estimated. A value of 0.7 might be a good starting point.

Since most component surfaces - with the exception of unrendered masonry and natural stone facades - only have a moderate water absorption, they cannot imbibe all the offered water anyway. In these cases, an exact knowledge of the rain quantity is not essential (whereas the duration of the rain is still important) and estimates for the r.r.f. and the position-specific driving rain coefficients may be sufficient.

WUFI automatically determines the r.r.f. from the inclination and the construction type; a user-defined value may be employed as well.

Or to put it another way 30% rainfall is calculated to fall away leaving 70% to potentially absorb into the wall . Pebble dash would exclude most of that 70%. Look at the graphs again - rendered walls perform dramatically better than unrendered.

edanto wrote: »

Am I getting distracted by a red herring?

I wouldn't put it that way . you did ask a question and I did answer it.

But for a simpler guide- in 2006 I used 50mm ( 12 + 38 - U Value 0.45 ) insulated plasterboard on my North facing rendered wall. In 2009 I had some extra power points installed and no sign of mould. Understand that even in my case , in mid winter , interstitial condensation occurs. But not too much of it - the blockwork wall can safely absorb it to be dispelled later in summer.

What the authors studies are saying however is that had I used 80+12 ( U Value 0.27 ) then the insulation would keep the blocks cooler for longer and therefore the amount of condensation would increase and do so for a longer period over the year.

It is vital that gutters , renders , flashings etc are maintained to ensure that the wall is not otherwise load up with moisture.

To summarise

Its perfectly sensible for you to dry line if you don't have the €€€€ for EWI.
You will notice a BIG difference in comfort and reduced fuel bills.

edanto

sinnerboy wrote: »

What the authors studies are saying however is that had I used 80+12 ( U Value 0.27 ) then the insulation would keep the blocks cooler for longer and therefore the amount of condensation would increase and do so for a longer period over the year.

I see how they came to that conclusion, but I guess my amateur instincts make it hard to rely on their conclusion because I'm so dubious about the assumption that the wall would be as wet as a 0.7rrf suggests. I'll think on that a bit and decide what U value is best for my case. The house is fairly sheltered from driving rain, and mostly pebble dashed.

On another related question - what normally happens at the stairs with Internal insulation? I presume the nuclear option is to take the stairs out, insulate and put it back in, a little smaller than before. Is the normal option to just lay the insulation up to the stairs/wall join and trim it at the back so it sits over the skirting at the side of the stairs? It might look a bit weird, but sure not to worry.