Yet Another Internal Insulation Question

tedimc

Hi all - firstly, love the forum and have been snooping around for a while!
I have read quite a few pros & cons on the using internal insulation, but can't find a case similar to my own:

• In the process of closing a deal on a ~40 year old bungalow (with basement)
• House consists of 75mm cavity wall, with no insulation.
• I've to do considerable renovation works anyway (rewire, plumbing/heating, roof, kithchen, windows, etc.) so was going to go to town on the insulation while I am at it.
• Am considering putting in UFH, heat pump, MHRV and as much air-tightness as the bank will pay for.

AlthoughI am aware of external insulation, I was thinking of pumping the cavity andfixing >50mm (maybe 75/100mm) insulated plasterboard to all the externalwalls. I was considering the boards with the integrated vapour barrier or foilbacking. I believe I need the cavity pumped in order prevent cold bridgingwhere the internal walls tie into the internal leaf of the external wall.

I am planning on seeking professional advice on this, but would like to be well armed with my own info as I found a lot of so called experts are absolutely shocking.....

Has anyone concerns/advice on the approach above? I know external may be best, butam fairly confident the cost will be too prohibitive!

Thanks in advance for any help. No doubt I will be using this forum a lot!

sydthebeat

you may have come across a 'rule of thumb' that your internal insulation shouldnt be more than 1/3 of whats in your cavity. This is because the colder you make the internal block the more likely you will have condensation forming on the inner face of it.
This cause a problem because this condensate cannot ventilate away anywhere, thus the inevitable build up of moisture and the growth of mould etc, and the ensuing health issues.

the rolls royce answer is for you to get dynamic condensation risk analysis done on different solutions and see which works best for you.

To be honest i have to scoff at the idea of integrated vapour barriers in plasterboards because of the inevitable cutting and gaps that are left. Any retrofit drylining is going to leave gaps between teh boards and (a) other boards (b) existing walls (c) new cuttings for services etc.

If your bucket is water proof, but has holes in it, is it still going to hold water?

A 75mm cavity pumped with a 32.5 insulated plasterboard gives a u value of around 0.26, compare to the existing 1.58.
That like upgrading it to 2005 levels.

you could focus the difference in budget into getting the building blower door tested and making it more air tight, and thus better at holding in heat.

tedimc

Thanks sydthebeat for your quick response.

I remember reading about the 1/3 rule alright, but it had slipped my mind.

A "dynamic condensation risk analysis" sounds pretty sore on the wallet - who would do this, a BER assessor?

I am kind of skuppered so regarding achieving near passive house standard using the internal insulation. I'll follow your advise and look into investing the difference in air tightness!

Thanks!

sydthebeat

kingspan and aeroboard both do this i think, there are also design consultancy firms which carry this out. Our own practise dont as the software is quite expensive (WUFI)
but if you google wufi youll find irish companies who do it.

if you want to assess the renovation within the passive parameters you should consult with a passive designer for opinions.

MicktheMan

OP, you say you are going to renovate, amongst other items, your roof, floor, windows, heating, wall insulation, improve the airtightness & install mvhr.
If it was me, (and I do live in a 40 year old bungalow), I would get (and pay for) the best independent professional advice before starting out as it shouldn't cost much more to do a proper job close to passiv house standards wrt insulation, thermal bridge detailing, airtightness etc. If done properly the extra over costs will be retrieved very quickly with very low running costs.

There will be certain "features" of the bungalow that will determine the best form of insulation (for instance, is the cavity clean and how were the heads over the opes formed?)

Also, the professional should be able to advise on such things as the advantage of high thermal mass if the house is to be occupied during the day, for instance.

I would start with having a full heat loss survey done which includes an air tightness test to find all the current weaknesses and strengths of the house. The report should then include recommendations and specifications for the renovation work based on client input/preferences/budget, survey findings, building physics etc.

If you get the thermal fabric right then your heating solution gets very simple (and cheap) and your ongoing heating costs will be minimal.

sinnerboy

tedimc wrote: »

[*]I've to do considerable renovation works anyway (rewire, plumbing/heating, roof, kithchen, windows, etc.) so was going to go to town on the insulation while I am at it. [*]Am considering putting in UFH, heat pump, MHRV and as much air-tightness as the bank will pay for.

So a big project then. Budget Eu 1250 rough finish and Eu 1500 / 2000 showroom finish.

If that's too rich for your blood all in one hit then prioritize your spending. Imagine all your new kitchen and bathroom fittings and being skipped in 15 years time because statistically that's what will happen to them. And all the floor finishes you will agonise over will be skipped sooner than that.

So get the base build right. Don't use internal insulation. Pump your cavities , install external wall insulation and triple galzing and make the building air tight and get your ventilation strategy right.

Install budget completions and use your reduced running costs to save for the showroom finish / skip fodder.

tedimc

Thanks guys for the feedback -

So a big project then. Budget Eu 1250 rough finish and Eu 1500 / 2000 showroom finish.

Yes, big project alright - but budget is more in the order of 750. I know thats well under-cooked, but we will prioritize rooms for finish and am doing a lot of the work myself. The house is on a great site and have actually admired it for years.

I'll post my planned list of works in another post/at another time, as I'm not quite ready for the questioning of my mental state at the moment.

Sinnerboy - yes am going to prioritize exactly as you say, so might re-visit the external insulation again. I'd have concerns over the lasting integrity of it over the years, but will look at the numerous posts on here about it.

Micktheman - was planning on getting a survey done alright and was interested in the thermal imaging. I'll have to get looking up who has expertise in these areas close to me.

Thanks again guys.