Cavity wall insulation help

gooseygander

Spec of our new build for a 2700sq ft house is one of the following as recommended by arct.
1. 100mm outer leaf, 140mm cavity with 120 rigid insulation, 100mm inner leaf, 62.5mm internal warmboard.

option 2. 100mm outer leaf, 200mm cavity with full fill pumped bead insulation, 100mm inner leaf.

We need to make a decision on the above asap and any informed opinions are most welcome. Had been originally going to go with ufh and air to water heat pump, but are now leaning towards oil rads, stove with back boiler and solar panel for summer hot water. spec 1 above was first suggested and spec 2 after I demanded a second option being worried about mould, condensation, thermal mass etc.etc
PLEASE HELP and thanks in advance

sydthebeat

who suggested the first spec?

Do you know you must have a preliminary DEAP assessment (BER) carried out before you commence... and that whatever option you suggest above will have knock on effects on other parts of the build?

gooseygander

sydthebeat wrote: »

who suggested the first spec?

Do you know you must have a preliminary DEAP assessment (BER) carried out before you commence... and that whatever option you suggest above will have knock on effects on other parts of the build?

Thanks Syd, both the above specs were suggested by architect/engineer. Don't think we have had any BER carried out and our commencement notice is lodged. Our planning was originally granted nearly 7 years ago at this stage and we applied for an extension after 5 which was granted so I am not sure if this answers your question. I know that the foundations and window cills and other knock on effects will have to change if we go with a 200mm cavity, but am just wondering which option is best in your opinion. Thanks again

gooseygander

gooseygander wrote: »

Spec of our new build for a 2700sq ft house is one of the following as recommended by arct.
1. 100mm outer leaf, 140mm cavity with 120 rigid insulation, 100mm inner leaf, 62.5mm internal warmboard.

option 2. 100mm outer leaf, 200mm cavity with full fill pumped bead insulation, 100mm inner leaf.

We need to make a decision on the above asap and any informed opinions are most welcome. Had been originally going to go with ufh and air to water heat pump, but are now leaning towards oil rads, stove with back boiler and solar panel for summer hot water. spec 1 above was first suggested and spec 2 after I demanded a second option being worried about mould, condensation, thermal mass etc.etc
PLEASE HELP and thanks in advance

Still interested in any opinions or reasoning or knowledge on above options ?

Superdaddy

I would go with option 2, keep your insulation in one place. It also makes sense when trying to add fitting to the interior walls. I am interested to know why you have gone away from the A2W heating.

topcatcbr

Of the two options I'd go with the 2nd. For the same reason keep all insulation in the same place. However I'm a fan of EWI external wall insulation but this has to be designed for to make it a good option.

It might be worth considering.

BryanF

option 2

hexosan

I'd increase option 2 to a 250mm pumped cavity

gooseygander

Superdaddy wrote: »

I would go with option 2, keep your insulation in one place. It also makes sense when trying to add fitting to the interior walls. I am interested to know why you have gone away from the A2W heating.

Just reckon I will go with the tried and tested. Good insulation, good stove with back boiler, condenser oil burner, solar panel for summer water. Any probs with oil and regular plumber can sort out same, cant say the same for air to water,also I feel all fuel markets are driven by oil prices anyway and the electricity is on the rise also. That's just my feelings at the minute but a small bit undecided at the same time.

Superdaddy

gooseygander wrote: »

Just reckon I will go with the tried and tested. Good insulation, good stove with back boiler, condenser oil burner, solar panel for summer water. Any probs with oil and regular plumber can sort out same, cant say the same for air to water,also I feel all fuel markets are driven by oil prices anyway and the electricity is on the rise also. That's just my feelings at the minute but a small bit undecided at the same time.

I see where you are coming from, are you going to use radiators too? If you insulate well enough you may not need very much oil at all, especially if you also have a wood burning stove with a back boiler. But heating systems all costs money, you have belt, braces and long John's with that amount of insulation. But will you ever use it or need it all? Are you going to have much solar gain? If it was me I would choose one of your heating systems and let the insulation and solar gain do the rest.

Green farmer

I retrofitted a room in my house last year with the insulated internal plasterboard slab. Increased room temperature by two degrees. They really are a good job.

gooseygander

Superdaddy wrote: »

I see where you are coming from, are you going to use radiators too? If you insulate well enough you may not need very much oil at all, especially if you also have a wood burning stove with a back boiler. But heating systems all costs money, you have belt, braces and long John's with that amount of insulation. But will you ever use it or need it all? Are you going to have much solar gain? If it was me I would choose one of your heating systems and let the insulation and solar gain do the rest.

Yea going with rads and not ufh an I am thinking the stove with back boiler will heat the downstairs living area and have just a few rads off it to the bedrooms upstairs. The oil will be back up for cold times for the whole house or simply when stove is not lit. The solar is just planned to heat a water tank to provide summer water (don't think they are much use in winter). Have not priced above system yet but that's my plan at the minute. The above should be cheaper than an air to water system I think, however I have not done the maths yet.

joeirish

gooseygander wrote: »

Yea going with rads and not ufh an I am thinking the stove with back boiler will heat the downstairs living area and have just a few rads off it to the bedrooms upstairs. The oil will be back up for cold times for the whole house or simply when stove is not lit. The solar is just planned to heat a water tank to provide summer water (don't think they are much use in winter). Have not priced above system yet but that's my plan at the minute. The above should be cheaper than an air to water system I think, however I have not done the maths yet.

Sounds similar to what I'm planning. But still not sure whether to go with rads or UFH. My idea is that if the price of oil goes ballistic in a few years and technology for heat pumps continues to improve I can then swap the oil boiler for a heat pump. And going for a large buffer tank, at least 500 litres so that I can store some of the heat from the stove and solar panels.

gooseygander

joeirish wrote: »

Sounds similar to what I'm planning. But still not sure whether to go with rads or UFH. My idea is that if the price of oil goes ballistic in a few years and technology for heat pumps continues to improve I can then swap the oil boiler for a heat pump. And going for a large buffer tank, at least 500 litres so that I can store some of the heat from the stove and solar panels.

I figure that if oil prices go ballistic then all other heating sources will follow suit anyway. I am no expert but all I have read is that ufh is very expensive system to run with oil so as I said gonna stick with tried and tested. However what is good for the goose may not be good for the gander (boom boom).