What difference did installing insulated plasterboard make

kdruce

Hi,

I am thinking of installing insulated plasterboard. Something like King span K118.

Has anybody got any experience of what difference in warmth, the insulated plasterboard made to the room? My rooms are not damp but the house is a little chilly as it was built in the 60s. I already have cavity wall insulation and good insulation in the loft. The floor is concrete, but I have already put thick underlay underneath the carpet.

I know it will make the room a bit smaller.

Regards, Kevin.

FreeBear

Can't comment on insulated plasterboard as I've not used it. What I have done is to use Celotex.Kingspan boards topped off with plasterboard on a couple of walls here. A wall in the stairwell got 65mm of insulation (plus 12mm PB), and a small box room got 75mm (three layers of Celotex and 12mm PB). Well worth doing. The box room is very much easier to heat, and the loss of floor space is not noticeable.

As you probably have a cavity wall, 50mm of Celotex/Kingspan will get you up to current Building Regs. I have solid brick on the upper half, so 75mm is needed. In terms of costs, I did the bulk of the work myself, so only really need to account for the materials when it comes to deciding if the Return on Investment is worthwhile. If I had to pay someone to do all the work, it probably wouldn't have been worth it.

dunstonh

We dont have insultated plasterboard but we did have the plaster taken back to brick, then insulation put on internally and then boards on top, in some of the rooms and those rooms are warmer than the rooms we haven't done it in (yet).  So, whilst not exactly the same thing you are looking at, it is the same concept.

markin

Fridge walls are only 30/40mm, Yes it would make a huge difference, So 50mm would almost be doubling your insulation.

kdruce

Thanks for the constructive information. I will get on with it. 

I must admit I think this stuff should be vat free or something to encourage people to do it.

FreeBear

kdruce said:

Thanks for the constructive information. I will get on with it. 

I must admit I think this stuff should be vat free or something to encourage people to do it.

Insulating materials are currently zero rated for VAT but only if you pay an approved contractor to install the stuff (at inflated prices) - There are a few other conditions that need to be met.. But for most installations, the cost of the materials is a relatively small part of the overall budget. I've spent less than £500 for enough Celotex to do all my walls.

A couple of tips if you decide to do the work yourself - Look up the "warm batten method" for fixing the insulation & plasterboard to the walls. Above the windows, use a strip of plywood (say 150-200mm wide) so that you have a solid surface to fix curtain rails to. Assuming you have decent DG windows, move the radiators to an internal wall. If the rads must remain under the window, attach sturdy battens to the wall to take the weight. Wrap 25mm of insulation round the window reveals to kill cold spots (one spot that insulated PB is good for).

j.a.mcguire

I was thinking of insulating my pitched roof with kingspan, just to try to reduce the cold air escaping up through the loft.  Has anyone seen good results from doing this?  The loft space has until now been a cold roof, and I was not intending on using it as an additional room.

kdruce

FreeBear said:

kdruce said:

Thanks for the constructive information. I will get on with it. 

I must admit I think this stuff should be vat free or something to encourage people to do it.

Insulating materials are currently zero rated for VAT but only if you pay an approved contractor to install the stuff (at inflated prices) - There are a few other conditions that need to be met.. But for most installations, the cost of the materials is a relatively small part of the overall budget. I've spent less than £500 for enough Celotex to do all my walls.

A couple of tips if you decide to do the work yourself - Look up the "warm batten method" for fixing the insulation & plasterboard to the walls. Above the windows, use a strip of plywood (say 150-200mm wide) so that you have a solid surface to fix curtain rails too.  Assuming you have decent DG windows, move the radiators to an internal wall. If the rads must remain under the window, attach sturdy battens to the wall to take the weight. Wrap 25mm of insulation round the window reveals to kill cold spots (one spot that insulated PB is good for).

Gosh £500 is cheap. I was planning to install the insulation myself so I guess I would have to pay vat. Unless you have any suggestions?

i was planning to use the Kingspan and Celotex products that have a vapour barrier, so you can glue them directly to the wall.

FreeBear

kdruce said: i was planning to use the Kingspan and Celotex products that have a vapour barrier, so you can glue them directly to the wall.

If you use the "standard" Celotex/Kingspan type boards, the aluminium foil should act as a vapour control layer. Tape the joints and patch any dings. You could use a sheet of plastic as a belt & braces backup. Oh, and don't rely on just adhesive to hold the boards on the wall. You should always use mechanical fixings to be sure.

I'm using multiple layers of 25mm board, all joints foamed and taped. No secondary VCL.

j.a.mcguire said:

I was thinking of insulating my pitched roof with kingspan, just to try to reduce the cold air escaping up through the loft.  Has anyone seen good results from doing this?  The loft space has until now been a cold roof, and I was not intending on using it as an additional room.

You would be better off putting down 250-300mm of fibreglass loft insulation between/over the joists. The loft space should be cold & draughty to minimise the risk of damp & rot. Insulating between the rafters would compromise the natural ventilation. In addition, no point in having a space that is (relatively) warm if it is not being used. Keep the heat in the rooms where it is needed.

Raxiel

Our house is an odd, prefab construction with (originally) a single skin of precast concrete downstairs and a timber frame upstairs, plaster inside, roof tiles outside, and a very thin layer of rockwool in-between.

The precast was replaced with an insulated cavity brick/block wall 20 years ago, but the upstairs still had nothing but that 70 year old thin layer of deteriorating rockwool.

We got internal insulation fitted this last summer. They fitted 62mm board (50mm insulation) to all the external walls.

Its made quite a difference to the temperature in these cold snaps. It used to be that downstairs was consistently warmer, despite heat rising, but now that's reversed and we use a lot less gas. Average temperatures have been a little lower here, and we've turned the thermostat down a bit, so an exact comparison is difficult, but on average we've saved between 20%-30% on our gas consumption since October, compared to 2021.

We used to get persistent mold problems due to condensation in sheltered corners. They haven't returned. It also blunted the impact of the heatwaves last summer which was a blessing.

Of course, it did result in a reduction in the internal volume of the rooms, but properly decorated you really don't notice it. We paid a bit extra to have the old board stripped off so the frame and old insulation could be inspected, as well as allowing me to run Ethernet throughout the house, but in retrospect it wasn't really necessary.

I don't know how good of a deal we got. My own calculations put the price of sourcing my own board around £1k last summer. We were quoted £3.5k for simple over-boarding and £5k to also strip back the old stuff. That company won by virtue of being the only one to actually give us a quote after almost a year of shopping around.

From a purely financial position, even with the increase in gas prices it will take a long time to pay for itself, but we were desperately overdue for re-decorating and the old plaster / paint job was in a terrible state even without the mold. Paying to fix that without dealing with the underlying problems with warmth and damp seemed like a false economy, and the house was pretty cheap even for the area in the first place, so I don't regret getting it, just wish we'd got it sooner.

consumers_revenge

Raxiel said:

Our house is an odd, prefab construction with (originally) a single skin of precast concrete downstairs and a timber frame upstairs, plaster inside, roof tiles outside, and a very thin layer of rockwool in-between.

The precast was replaced with an insulated cavity brick/block wall 20 years ago, but the upstairs still had nothing but that 70 year old thin layer of deteriorating rockwool.

We got internal insulation fitted this last summer. They fitted 62mm board (50mm insulation) to all the external walls.

Its made quite a difference to the temperature in these cold snaps. It used to be that downstairs was consistently warmer, despite heat rising, but now that's reversed and we use a lot less gas. Average temperatures have been a little lower here, and we've turned the thermostat down a bit, so an exact comparison is difficult, but on average we've saved between 20%-30% on our gas consumption since October, compared to 2021.

We used to get persistent mold problems due to condensation in sheltered corners. They haven't returned. It also blunted the impact of the heatwaves last summer which was a blessing.

Of course, it did result in a reduction in the internal volume of the rooms, but properly decorated you really don't notice it. We paid a bit extra to have the old board stripped off so the frame and old insulation could be inspected, as well as allowing me to run Ethernet throughout the house, but in retrospect it wasn't really necessary.

I don't know how good of a deal we got. My own calculations put the price of sourcing my own board around £1k last summer. We were quoted £3.5k for simple over-boarding and £5k to also strip back the old stuff. That company won by virtue of being the only one to actually give us a quote after almost a year of shopping around.

From a purely financial position, even with the increase in gas prices it will take a long time to pay for itself, but we were desperately overdue for re-decorating and the old plaster / paint job was in a terrible state even without the mold. Paying to fix that without dealing with the underlying problems with warmth and damp seemed like a false economy, and the house was pretty cheap even for the area in the first place, so I don't regret getting it, just wish we'd got it sooner.

Cornish unit?