Cavity insulation or insulated slab

swampman1

Hi
starting a 70 sq m extension soon an just wondering when building will i build blocks leaving a cavity standard practice. Or as iv seen lately 4' solids on flat battened on inside an insulated slab. thanks in advance

MicktheMan

swampman1 wrote: »

Hi
starting a 70 sq m extension soon an just wondering when building will i build blocks leaving a cavity standard practice. Or as iv seen lately 4' solids on flat battened on inside an insulated slab. thanks in advance

You will need to comply with current building regs so get proper professional (i.e. paid for) advice asap.

swampman1

thanks. my architect gave me an option of the two. he said some builders are goin the solid block, slab route instead of using cavity. the room will heat up quicker instead of heating the inner block.

MicktheMan

swampman1 wrote: »

thanks. my architect gave me an option of the two. he said some builders are goin the solid block, slab route instead of using cavity. the room will heat up quicker instead of heating the inner block.

Then, have your architect go through each option in detail with you and explain to you the pro's/con's.

swampman1

was looking for somebody elses opinion on it rather than just architect. to see wat other people thought.

Remouad

Why not both?
You can never have too much insulation.

murphaph

Speaking as a layman I'd imagine there are special considerations with an extension. You could insulate the exterior of the new structure to the latest and greatest standards but if it's extending a 70's cavity block built house with no insulation in the walls at all then the energy will just flow through the existing building and out through its walls, completely bypassing your top of the line new insulation. Interesting topic.

MicktheMan

swampman1 wrote: »

was looking for somebody elses opinion on it rather than just architect. to see wat other people thought.

Plenty of thoughts have been expressed already in this forum. Use the forum search function.:)

MicktheMan

Remouad wrote: »

Why not both?

Not a good idea. Insulation should be in one plane

Remouad wrote: »

You can never have too much insulation.

You can if it's in the wrong place

Idbatterim

whats wrong with putting up kingspan etc internally?

MicktheMan

I'm not going to go into it here but there has been a lot of discussions on this over in the Construction & Planning forum. Using search terms such as drylining, interstitial will get you loads of info.

swampman1

thanks for replys. read some of the other forums. basically what im asking is, im building a 4' solid block wall on the flat wit no cavity, battened wit 2 by 1 an then 92.5 mm insulated slab 80 mm insulation. k 17 kingspan board i tink. this will be the only insulation on walls. is that enough

Idbatterim

hey op, received this from build4less by email a few days ago. Might be of interest...

SECONDS Insulated PIR/Polyiso Kingspan Plasterboard

Limited Seconds available


measurements are 2400mm x 1200mm with very slight damage


Available


38mm €17.85 each +vat (46 available)


62mm €20.47 each +vat (34 available)


32mm €15.00 each +vat (40 available)


38mm phenolic €20.50 each +vat (250 available)


62mm phenolic €22.50 each +vat (50 available)


contact Nora Smith at Build4less on tel. 0579100598

Build4less @build4less
Insulated slabs seconds are available at Build4less. Almost perfect and knockdown prices. Call us for a price. Tweeted on 15th September...

swampman1

thanks for that. was actually looking at a renovate show the other day and the builder went to the manufacturer of the slabs an got the seconds from their for little or nothing. a huge saving for near perfect slabs.

Outkast_IRE

Would prefer a wide cavity any day myself rather than insulated slabs.

Not going to list the reasons again but have a look in the construction forum this question has been asked plenty of times.

I understand to an extent why some people pick insulated slabs when renovating , but for the life of me I can never understand why you would pick them in a new build, the wide cavity full filled with insulation is the superior option.

swampman1

and the reason been. as in a 150 cavity pumped and sand an cement finsh an them skim, are you not heating that and the block to keep the heat in. rather than the insulated slab, less to heat to keep the heat in.

MicktheMan

swampman1 wrote: »

thanks for replys. read some of the other forums. basically what im asking is, im building a 4' solid block wall on the flat wit no cavity, battened wit 2 by 1 an then 92.5 mm insulated slab 80 mm insulation. k 17 kingspan board i tink. this will be the only insulation on walls. is that enough

Enough for what?

- Compliance with Part L of building regs?
- Acceptable risk of mould growth at back of insulation?

These q's cannot be answered in isolation. To answer them you will need the input from a professional who will look at the project as a whole and advise.

swampman1

which in your opinion, ie, the people reading, if they were building in the morning what option would they go for.
1) cavity
2) solid block

MicktheMan

swampman1 wrote: »

which in your opinion, ie, the people reading, if they were building in the morning what option would they go for.
1) cavity
2) solid block

Number 2 and externally insulate.

Outkast_IRE

swampman1 wrote: »

and the reason been. as in a 150 cavity pumped and sand an cement finsh an them skim, are you not heating that and the block to keep the heat in. rather than the insulated slab, less to heat to keep the heat in.

Yes you heat up the block and sand and cement this gives thermal mass which is a positive in my opinion.


Lets talk about thermal comfort and the feeling of warmth or coolness in a room. Most people assume you use heating to raise the air temperature in the room and bingo you have a warm comfortable room. When in fact that's not true at all.

The air temperature and the mean radiant temperature at any point in the room are as important as each other. For example your radiator heats to 60 degrees but its small in size, and it raises the air temperature to 21 degrees. All well and good, next step the increased air temperature and some of the radiant heat from the radiator starts heating the various surfaces in the room eg, walls, ceilings,floors and windows. And this is where the scenario will differ depending on your insulation method.

If you insulated internally, the plasterboard will absorb some of this heat and the insulation will be highly resistive to heating up. So your left with decreased thermal mass, which isn't a big deal until you turn off the heating, if your house is correctly ventilated by passive vents, then the outside cooler air will replace the warm interior air, once the air temperature drops beneath the temperature of the walls, the heat the plasterboard absorbed will be given back to the room but because you insulated internally there is not actually that much heat to radiate back due to low thermal mass . So you notice drop in temperature quicker than in a house with the insulation located in cavity or external.

In a house with the cavity filled and blocks on the interior , the heat contained within these blocks will radiate out back into the room for a significantly longer time, which ultimately means for the user greater thermal comfort.