Cost of Extension

kco3d

Hi,

I'm hoping someone could give me a rough costing for an extension to a mid-terrace house with the following details,

Single story 23 sq m
Cavity wall construction 100/100/100 with 60mm insulation
100mm floor insulation
pitched roof with 200mm insulation

Understand that more labor involved with it being mid-terrace and cost can vary a lot depending on spec. I have heard a few people in the trade say around €1000/sq m. Would people here agree with this figure for a basic build with the spec above?

Thanks,

Handsandtools

I say 1000e/sq.m, Your 100/100/100 +60mm insulation, ''K8'' Kingspan 60mm in cavity and 32mm koolterm17 or 50mm insulation inside will give you u-value of wall 0.19 . If you will put 60mm inside than it will be more than needed. 2011 Building reg. part L Walls 0.2W/m2K roof 0.16W/m2K.
Any roof windows?
Extra heated space,
All these small thinks can add or reduce Your cost, but average is 1000e/sq.m.
Consider that today You can get better spec and more energy efficient building for same price as 4 years ago.

Bubbling

First off, you really need some professional advice (architect, engineer) so that what ever you build is designed to meet the minimum thresholds of the building regulations. The specification you have provided is out of date! Very worrying!

Cost wise, for an extension I would advise on €1350/sq.m. to €2000/sq.m. I imagine €1000/sq.m. excludes finishes and kitchen, sanitary ware, etc. It would at best give you a weather tight shell - "a builders finish". A builder might quote you €1000/sq.m. but then he may say I never priced tiles, etc.

You need to budget properly - not just pick the lowest figure possible.

A typical architectural-designed medium level extension, with a standard kitchen, say 40m2, would be around the €65,000 / €70,000 level.

Don't build cheap. Don't design on the cheap either. A good design, construction, building, thermal performance will deliver value to you.

DOCARCH

Bubbling wrote: »

Cost wise, for an extension I would advise on €1350/sq.m. to €2000/sq.m.

Agreed, especially for a 23 m.sq. extension.

The bigger the build, the less per m.sq. the cost tends to be (economies of scale). I would only expect (hope) to see € 1000/m.sq. on a large (say 100m.sq. + extension).

Handsandtools

Bubbling wrote: »

First off, you really need some professional advice (architect, engineer) so that what ever you build is designed to meet the minimum thresholds of the building regulations. The specification you have provided is out of date! Very worrying!

Cost wise, for an extension I would advise on €1350/sq.m. to €2000/sq.m. I imagine €1000/sq.m. excludes finishes and kitchen, sanitary ware, etc. It would at best give you a weather tight shell - "a builders finish". A builder might quote you €1000/sq.m. but then he may say I never priced tiles, etc.

You need to budget properly - not just pick the lowest figure possible.

A typical architectural-designed medium level extension, with a standard kitchen, say 40m2, would be around the €65,000 / €70,000 level.

Don't build cheap. Don't design on the cheap either. A good design, construction, building, thermal performance will deliver value to you.

At first it looks out of date, but when you look at different material options, you see that there's way to reach today's requirements with that spec.

sydthebeat

Handsandtools wrote: »

I say 1000e/sq.m, Your 100/100/100 +60mm insulation, ''K8'' Kingspan 60mm in cavity and 32mm koolterm17 or 50mm insulation inside will give you u-value of wall 0.19 . If you will put 60mm inside than it will be more than needed. 2011 Building reg. part L Walls 0.2W/m2K roof 0.16W/m2K.
Any roof windows?
Extra heated space,
All these small thinks can add or reduce Your cost, but average is 1000e/sq.m.
Consider that today You can get better spec and more energy efficient building for same price as 4 years ago.

the bolded bit is a bad specification, and offers a significant risk of interstitial condensation on the inner block with associated mould and health problem.

BryanF

Handsandtools wrote: »

I say 1000e/sq.m, Your 100/100/100 +60mm insulation, ''K8'' Kingspan 60mm in cavity and 32mm koolterm17 or 50mm insulation inside will give you u-value of wall 0.19 . If you will put 60mm inside than it will be more than needed. 2011 Building reg. part L Walls 0.2W/m2K roof 0.16W/m2K..

Where is the dew point in your spec above if you have 60mmPIR in cavity and 50mmPIR drylining?

As this is an extension the regs should be quoted from other column in TgdL2011

Edit: syd got there first

kco3d

Many thanks to everyone for the replies.

Bubbling wrote: »

First off, you really need some professional advice (architect, engineer) so that what ever you build is designed to meet the minimum thresholds of the building regulations. The specification you have provided is out of date! Very worrying!

Cost wise, for an extension I would advise on €1350/sq.m. to €2000/sq.m. I imagine €1000/sq.m. excludes finishes and kitchen, sanitary ware, etc. It would at best give you a weather tight shell - "a builders finish". A builder might quote you €1000/sq.m. but then he may say I never priced tiles, etc.

You need to budget properly - not just pick the lowest figure possible.

A typical architectural-designed medium level extension, with a standard kitchen, say 40m2, would be around the €65,000 / €70,000 level.

Don't build cheap. Don't design on the cheap either. A good design, construction, building, thermal performance will deliver value to you.

Bubbling, what I'm planning for is pretty much a "builders finish". Its just a room at the rear of the house. No finishing required in terms of flooring, painting etc. The specs I provided above in terms of insulation are what builders have specified in their quotes. I haven't specified what I want in this regard. When you say this spec is out of date I get worried as this is what different builders have included. I understand the proper way of doing this is decide on a spec with your arch and give this to the builder to cost. If the spec provided above is out of date then is 1000 sq m. too little for what I'm looking for? The estimates I've received to date range from 32 -36k.

Handsandtools

BryanF wrote: »

Where is the dew point in your spec above if you have 60mmPIR in cavity and 50mmPIR drylining?

As this is an extension the regs should be quoted from other column in TgdL2011

Edit: syd got there first

What I say is 60mm pir in cavity and max 32 pir drylining or 50mm fiberglass + vapor barrier. 60mm inside is too much, because internal layer of insulation has to be max 1/3 of overall insulation, so the condensation point is as far at the back of vapor barrier.
You right,because of extension less than 40sq.m, but I believe all new built has to be built up to date, no point build new extension based on old standards.
You right tgL 2011, was late last night when typing.