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Filler like that never looks quite right. I tend to fill with mortar instead. not sure about the damp. Do you have a picture from the outside?

There are various different types of insulated render you can get - not sure how fire resistant they all are though. Tends to be quite expensive for the U value it gives but there might be something appropriate. Something like this (never used or heard of it before but seems to do well on fire resistance): https://proofshield.co.uk/products/internal-external-wall-insulating-plaster/

sorry if this has been asked before but why do you want gutters? Its not like the rain is going to run down onto the front deck - its all going off to the side.

Ok thanks Jack

Jack - couple more questions! My installation involves both supply/extract ducts terminating upwards into two pitched roof cowls. I know now that ideally the ducting would slope down to the main in/out penetrations but that wasn't really feasible here. Is it possible that is compounding the issue with condensation tracking down from the roof cowl? (my ducting is all insulated EPS ducts all inside the thermal envelope and there isn't really any sign of mould in these ducts its just in the unit itself) Having made the fix to yours have you been able to confirm that it is working in your case? Cheers John

Thanks for the diagram. Very helpful

So you mean something like a thin bit of corex (or thinner I guess as its already tight fitting the heat exchange in) that extends over to the side with the drain? (the right side of the unit in my picture). That makes some sense. I noticed another problem over the winter. I could hear the fans working hard and when I looked I found that the insect mesh on the ubbink roof cowl had iced up. Crazy that I was recommended a cowl with insect mesh that is far from accessible. Anyway I think I will have to try and remove the insect mesh in situ and rely on the MVHR filters to stop this happening again. Appreciate the help Jack.

not yet! just in discussion with my original suppl;ier

Regarding a heating source (sorry haven't read whole thread so assuming no water heating) - assuming it is a airtight/ well insulated why wouldn't you just use a small electric heater rather than the expense of an ASHP/GSHP. I had a SIPs built office similar size that I just used a small heater in and it was plenty.

why don't you tile it to the same level as the step?

Seems pretty straightforward to me - already has a decent bearing. Just take out the two courses below and make good. If the lintel is wood I would have thought you could clad the underside with some hardibacker or something like that. I used hardibacker as the register plate for my burner. But it looks like concrete lintel to me.

I sold some lying around at mine on gumtree in Oxford. I think they were off to Africa!

I wouldn’t bother with pva. also don’t make the mortar too wet if you are pointing (not rendering). You’ll just smear it everywhere and make a mess.

So i finally had a look and both fans appear to be working. No mould in the duct from the Brink unit to the extract terminal. I noticed that there is some standing water in a small section - in the second picture there is a small section to the left of the EPS upstand (so to the left of the drain and nearer the back) with no route for the water to go anywhere. When the heat exchanger is in place this section is separated from the fan with the mould issue. Any ideas?

Use small bits of stone/brick to fill voids as well as mortar. Shove/throw some mortar in, push in some small bits of stone/rubble. Apply more mortar if needed and depending on the finish you are going for.

Hydraulic lime is breathable and doesn’t go with cement. Hydrated lime is what is added to cement to make it more workable and can lighten the colour.

I thought I heard that if you are running UFH that the UFH pipework can effectively be the buffer tank but you are saying that is wrong. My situation is: small conversion (70m2) , just UFH downstairs running 4 loops of pipe but as one zone (no upstairs rads), heat pump (5KW region) for DHW and UFH, UVC upstairs by bathroom. I hadn't accounted for a buffer tank so might need to think where it could fit as space is tight. Can you advise: 1. What size of buffer tank would be suitable? 2. Is it best/easiest to put the buffer tank upstairs with the UVC or can it be put downstairs by the UFH manifold? thanks

Isn’t sound insulation the only useful type of insulation on a non external wall?

Fair point terry.

I’m not entirely sure that is true. There is a bit of a mystique about it but I’m not sure it is justified. It is just that cement has taken over for so long that most Brickies can’t cope with something new. For someone new to pointing I would say using lime is easier than cement since you have more time to play with. There are also a few other differences. Dampen the stone you are pointing, keep the wall damp/covered if you can after the mortar is in. I would go for hydraulic lime 3.5 and sharp sand (1:3). Getting the right amount of water is key for repointing. You want it dry enough to not smear over the stone. Make sure you rake out enough, push the mortar in firmly and don’t be too fussy to get it looking right. Wait (sometimes a day later if not too dry) till it is ready to rub over ( I use the back of a churn brush that I have shaped to suit the stone) and make sure it is all pressed into place properly. Wait again till it is ready to brush over (I use a soft brush as I don’t like seeing brush lines). I can see the appeal of lime putty as you don’t have to mix up but it is more expensive.

why bother with the plasterboard you aren't using? 75m insulation, battening, 15mm soundbloc? Is it the extra sound reduction?

I would put the strong boys a bit higher up and accept that you are going to have to do some remedial filling in above the concrete lintels. It might be hard to get the lintels in if the stongboys are this low since the angled support for the strongboy can get in the way and you also need room to get the lintel onto the mortar beds.

Sorry last question - are you saying that I can put copper into that push fit isolator and plastic out? Or do I still need a converter before it?

I feel like I’m back at school!

Is it ok to have copper going into a compression isolator and then plastic coming out? thinking like this........