Thursday, March 17, 2011

Suspended Underfloor Insulation

Guys, we bought a house that needs so much work.  And I had this stupid idea that I could try doing some of the work myself.  So I started going all DIY and stopped taking pictures of food.  (I still cook but not quite as much.  I'll get back to it soon.)  So will you forgive me while I talk about some of the non-food things I've been trying to make?  The first is suspended underfloor insulation.

I love older homes, but the floors are so drafty (by design).  I wanted to make our period property warmer and insulated the floor with suspended insulation.  I am posting this just because I looked all over the internet for a step-by-step and  couldn't find it.  Maybe my search skills need serious help. 

We bought a terraced house from 1920 that has the typical build for a British house of the time.  I don't know the technical terms, but the house foundation is made of bricks.  There are supporting walls that make up the rooms, and then in between there rows of little brick walls. About a meter above the ground the mini-walls stop and long joists rest on top of the bricks.   The floor is made up of floorboards laid across the joists and then nailed in place.  You want to see a picture of me demonstrating, right?  All the floorboards in the room have been removed and I'm standing down on the dirt between the mini-walls.

In order to insulate (oh, and repair some rotten joists), we took up all the floorboards.  I did this by removing the baseboards (skirting) with a crowbar and then carefully prying up each of the boards.  I wanted to lay the floorboards again so I numbered them and removed them carefully. (Some still broke.)  Also-these are photos from two different rooms.

Once all the boards were removed, I got breathable roofing membrane (PermaVent-it was cheaper on Ebay than anywhere I could find locally) and used duct tape to tape the individual sheets together.  I wanted to make a breathable, hanging "net" for the insulation.  I taped the front and back of all the adjoining pieces.  I made it big enough to allow for about six inches of insulation between each joist.

The goal was to allow the joists to still be exposed to the air from the vents but then to have breathable insulation on top.  (So the floorboards would have the benefit of the air without the cold drafts!)

We rolled the breathable membrane over the joists.

We used batons and screws to fasten the membrane to the wall.  We also used some spray foam in some of the gaps to prevent thermal bridging.  We wanted to allow the ends of the joists to still breath (and not touch the wall), but also to make the membrane layer as tight as possible.

Once about half of the membrane was fastened (we wanted to still have wiggle room to make adjustments as we started putting the floorboards on) we put back the first floorboard.  (This is where I was so glad for the numbers!)  I used floorboard brads from Screwfix, they're about 2 1/2 inches long.  We hammered them in by hand. 

We put a second board on and then starting pushing the insulation (it looks like dirt, but really it's loose fill insulation made from recycled newspaper that I got from the EcoCentre) under the floorboards.  So what we have is dirt, then about 2 1/2 feet of air, then the membrane draped over the joists, six inches of insulation and the floorboards on top.

We kept adding more boards and adding more insulation. 

And then filled the insulation to the end of the room.

And hammered in the rest of the boards.

The floorboards have been down for about four months and it has made SUCH a difference. Our house has been under renovation with no heating all winter (don't worry, we're in a rental) but these rooms still felt warm.  It was a huge pain and because I'm so slow and I waited for the salvage yard to get the right replacement boards it took about two months.  But (as long as we did this right and the wood stays nice and dry) I am so glad we did it.  


Bek said...

mitch, what can't you do?

you're giving me a complex!

you my guru!

someguystu said...

Hi...any update on this? I've heard that breather membranes can sometimes pool water and some say they should be installed on the warm side (for walls anyway). All ok 3 years on?

Mitch said...

Unfortunately, we moved and I don't know how the insulation has fared! In our new home, we put in underfloor insulation again, but this time with netting...