Why IWI instead of EWI?

And what is "2.O overall gap"?

If the aim is to make it comfortable first rather than energy efficient as the main aim then increase the loft insulation as a first quick win then reduce or eliminate the drafts. You say there are old aluminium framed windows consider replacing these with reasonable plastic ones and probably the front and back door as well as part of the draft prevention and comfort plan. You may or may not decide wall insulation is worth the effort/cost.

Quick figures for EWI or IWI 5 cm = 0.5, 8cm = 0.35 and 10cm = 0.29 U values. Just a thought - if you go down the route of insulating walls do you fall foul of the building regs that require you upgrade to current standards if you do more than a %age of a building element? If so you will need about 130 mm of EWI or IWI. (doing nothing gives a U value of 1.72)

Posted By: djhWhy IWI instead of EWI?

+1
EWI is better than IWI and as it is a bungalow it should be possible to do it from a ladder rather than scaffolding (which makes it cheaper and possible where there is limited room to the neighbours. Put on EWI to a thickness that is manageable with the existing eaves. EWI is DIYable you might want to get the adhesive/mesh coat put on by a professional but after that the top decorative thin film render coat can be substituted by a good quality masonry paint which is quicker, much cheaper and easier to DIY.

But to answer your question

Posted By: ArtiglioIs it possible to bond insulated board direct to the existing wall?

Yes, but issues arise with electrical fitting (plugs and light switches) perhaps more so than with battens because there is no service void for new cabling and you can't guarantee enough spare cabling to pull the fittings forward to the new surface. EWI is much less disruptive than IWI.

IWI will give a quicker and more responsive heating but suffers from the lack of stability afforded by the thermal mass of brick walls. As the bungalow will be permanently occupied by a pensioner stability would be important rather than for someone out at work all day who wants the place to heat up quickly 20 mins before they get home. (My mother had her heating set to 21 deg. and then 22 deg when she got a bit older and this was set 24/7 365 days, it worked for her).

The thermal bridge at floor level can be mitigated by skirt insulation, either following down the outside of the foundations, or horizontally outwards from the wall. Or if you're as keen as wookey was, you can replace a course of bricks with marmox blocks.

Posted By: Peter_in_Hungarythe top decorative thin film render coat can be substituted by a good quality masonry paint

Really? In Hungary, but in UK? That's a new one on me.

Posted By: fostertom

Posted By: Peter_in_Hungarythe top decorative thin film render coat can be substituted by a good quality masonry paint

Really? In Hungary, but in UK? That's a new one on me.

The thin film render normally applied is a decorative weather proofing protection for the EWI beneath. The same properties can be obtained with a good quality silicon masonry paint (both need primers). The downside of masonry paint is that it is not so good at hiding an imperfections in the adhesive/mesh coat (e.g. imprint of the mesh showing on the surface).

Posted By: Peter_in_Hungarydownside of masonry paint is that it is not so good at hiding an imperfections in the adhesive/mesh coat

Oh I see - I took it that you meant masonry paint direct on the EPS, instead of the whole thin-coat render system. 'As you were' then.

Posted By: ArtiglioIn respect of the thermal mass aspect, mums always been one for open windows and doors if there even a hint of sunshine, that may change as the years pass and she becomes less active. So a quick reheat will ne beneficial for those evenings when temps drop quickly at the end of a warmer day.

If she gets MVHR she will hopefully feel less of a need to open windows all day long. My wife likes to open the bedroom window in the morning whilst she gets up, but accepts it's better to keep it closed most of the time. Thermal mass means the room stays reasonably warm throughout.

Think we've discussed that a few times with therm modeling : to act as a coffer dam and extend heat flow path lengths meaningfully, the skirt insulation has to extend a metre or so down below ground level. But foundations of 1915 bungalows not typically that deep.

Posted By: ArtiglioGood day all

My mother ( mid 80’s years old) is downsizing and we’ve purchased a small 1920’s bungalow , it’s pretty much untouched in terms of insulation since it was built. Basically only 100mm of fibreglass in the loft.

I’m struggling to find a definitive guide to iwi with insulated plasterboards. Rooms are small and we don’t want to loose too much space.

Wall construction is 9” flettons, painted pebble dash on 3 sides, 4 side has only 700mm to neighbours wall and the eaves and guttering mean there is only a 6” gap. Gutters have been cleaned and leaky joints fixed.

Like everyone else I would encourage you to think again about EWI. I started off doing IWI because it was easier to DIY, but the more I learned the more I wished I had just done EWI all round. My house is now half and half. It works but it is sub-optimal.

Your house is already rendered so after EWI will look just the same, so no planning issues.

On the wall with narrow access, you could just reduce thickness up to head height and have a some IWI to compensate. Or just IWI that wall only if need be. (I don't understand how it's 700mm to the wall, but there is only a 6" gap? (why not a 700mm gap, which is awkward but sufficient - easier with a bonded-only system than one needing mechanical fixings as drill+ bit may not fit?) )?

EWI is much better for thermal bridges, less disruptive, doesn't take away from room space. Keeps thermal mass on the inside. And is no harder to do, except it's generally best to get a professional renderer for the top layer. Woodfibre (above grade) or EPS.

I’m struggling to find a definitive guide to iwi with insulated plasterboards. Rooms are small and we don’t want to loose too much space.

If doing IWI I normally advise against insulated plasterboard. You want the insulation and plasterboard to be separate so that you can properly airtight the insulation before covering it up. It is impossible to do this when the layers are combined. If you did the airtightness first (e.g. painting the walls with latex paint (such as blowerproof)) then insulated plasterboard would be OK. But on a solid walled building you don't really want the EPS/XPS/PUR/Phenolic insulations those come with anyway. Woodfibre (or cork plaster) is a much safer bet for solid-walled buildings, giving you a vapour-permeable wall construction.

On a solid wall building I would always default to woodfibre boards then plasterboard (or lime-based plaster) on top. Backtoearth has loads of videos and info on how to do this DIY. It's not hard.

Is it possible to bond insulated board direct to the existing wall? If so i can use a thicker board than if I were to use a battened system.

Yes you can just bond insulation directly to the wall. That's how I did mine. Battens under insulation are generally dumb, and just allow thermal bypass. Battens _on top_ of boards under plasterboard do provide a useful service cavity, (and you can put fluffy insulation in that so it's not wasted space). This is much easier to do in a thermal-bridge free way with nice solid insulation like woodfibre boards, than things like PUR and EPS which will not take fixings.

There will be mvhr . Heating is going to be gas combi boiler.

MVHR is an excellent plan. Fitting a new gas boiler at this stage should already be illegal IMHO. Get a heat pump. The difference in emissions over the system lifetime is enormous and it will be cheaper to run. If you are starting from scratch you have the opportunity to make a really comfortable system with UFH.

At least that’s the plan, i’m struggling a bit to find an easy to understand comprehensive guide to what i should be doing . Can anyone point me in the right direction?

This guide from Cambridgeshire council is pretty good as an overall retrofit guide: https://www.cambridge.gov.uk/media/st3c1mdf/retrofitting-your-home-report-non-accessible-version.pdf

Not sure if that is what you are looking for? Perhaps you want more detailed info on each of the actual measures?

HTH

Thanks for raising that, Tom. I don't always sign in, but I note that when I sign in I see whispers. In the 'old days' only the one to whom it was whispered would see it (which would be Wookey in this case!!)

Wookey, if you are signed in you will see 'edit', 'delete' and 'quote' at the top RHS of your msg. (Indeed I can see it there). I have just done a post as a test and pressed 'delete' and it did just that.

Sounds like yet another 'feature' that doesn't work for all browsers I can only see edit and quote as well. Twas ever thus; traditionally we deleted posts by making them whispers to ourselves, but that isn't reliable now either! Second favourite would be to make your post a single '.'

In the 1990's I insulated using insulated plasterboards, 2" total thickness, inside 9" solid walls.

At the time I had little knowledge and relied on a small A4 quarter inch thick publication from the Building Research Establishment about The energy efficient renovation of houses. Plus a plasterer I knew.
We used dabs plasterboard adhesive and used a 4" x 4" about 4 foot long to line things up and spread the dabs for maximum contact of adhesive to board and wall. I've always had reservations about the amount of adhesion and it's longevity. We used hammer fixed stainless thin wall T-tubes to each sheet for fire safety, then skimmed.

It's still here and is a vast improvement over the original.

More recently, I believe, one uses lines of adhesive aound the rear of the board periphery rather than dabs to stop air flow twixt board and wall. Also the plasterer gobbed up (filled) odd bits of void causing cold breaks, I didn't know any better at the time.

I also changed the windows for slightly smaller ones to improve insulation in the window reveals. Internal walls are a cold break where they meet external walls. Possibly could have clad these part way into the room ? Too much faff. Similarly interior walls that extend into the roof void?

Over decades the odd crack has appeared as walls move. I'll re-skim and rectify the cold breaks

As you're experienced I don't think you can go wrong.

My mom has had grants for a new boiler and had her cavity wall insulation sucked out and re-installed, she the had a big radiator put in the room she lives and sleeps in. Rarely uses the heating, lol.