Hi
I have just insulated one room and the cellar / hall floors from underneath using the B&Q recycled plastic bottle insulation. It has an R value of 5 and is no itch. This was key as I had to lie under the suspended floor in a space of 700 cm tapering down to 100 cm so I was in intimate contact with the insulation. The draw back is the cost at £13.00 per roll. I now need to insulate the last room on the ground floor. This room has more clearance so I could fit rock wool as I will be able to avoid too much contact. B&Q do a Knauf 3 roll pack for £3.00 with an R value of 4.5. I don't think the 0.5 difference in R value will make that much difference (but I stand to be corrected) my main concern with the Rock wool insulation is will it need additional support. The no itch fitted nicely between the joists and was held in place with staples. It seemed to grip the rough wood. Does anyone know if the Rock wool will act in the same way or will I need to add netting or a membrane?

Many thanks in advance.

Dave

I have completed this job and decided to go with the cheaper insulation for the floor with the easier access. These are my observations for what they are worth.

The B&Q no itch fleece is made from recycled plastic bottles and it around £12.00 per roll. It is nice to work with and I am confident it will stay in place with staples.

The B&Q insulation at £1.00 a roll (£3.00 for a 3 roll pack) is made from recycled glass bottles and had a 0.5 lower R value. It was not a problem with itching (compared to Rockwool) but I did wear a mask as it was dusty. It was not as tight-knit as the fleece and I was not confident it would stay in place with staples.

In the end I put a double layer of the £1.00 a roll stuff and then used heavy duty weed control membrane being sold off by B&Q for £17.00 for 12m2 to hold it in place. This worked very well.

I have attached photographs of both approaches. I don't regret using the more expensive insulation in the other locations as having to add the membrane would have been very difficult due to limited access.

While you are under the floor it would be no harm to fix some 100mm sheets of EPS to the underside of the joists to eliminate the cold bridge through the joists, it will probably half the U-value.

Sorry about the images. They are only 300Kb in size but I get this error when I try to view them.

Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 3264 bytes) in /home/greenbui/public_html/forum114/extensions/InlineImages/image.php on line 14

Is there a different way to add photographs?

Thanks for the tip on the EPS.

Dave

Viking

The EPS tip is interesting. I have insulated my floor in a very similar way as Dave, again without using EPS.

But. I have used breather membrane to hold the insulation up with the membrane positioned so that water will fall out of the bottom but not penetrate upwards. If I then sandwich it in EPS then I will lose the value of the membrane.

Is this a danger or am I talking bollocks? The space under the house is very well insulated and there is no way that water can get in. I have speculated since doing it that the membrane was a bit of a waste of money as I could have held it up with sheeting really.