Is this wood sub floor on top of concrete?

[Robbot]

Hi, I have a bungalow that was built in 2001.

 

When I recently pulled the carpets up I noticed a series of routed inspection covers under which appears a damp membrane covering... 'heating pipe junctions'?. I don't want to cut the membrane if I can help it; however, would there be a concrete base and some form of insulation underneath the wooden subfloor?

 

I'm trying to understand the construction method.

[ProDave]

That is probably a suspended timber floor.  What does it feel / sound like if you stamp hard on the floor in the middle of the room or even jump up and down.?

 

If you hoover out the dust there is nothing wrong with cutting the membrane to have a look and taping it up again afterwards.

[Robbot]

There are no air bricks around the property, so I'm assuming there is a concrete floor below the wood.

 

The floor is suspended as I can feel slight movement, plus it has dropped by a few mm where one of the inspection covers was routed out across the T&G leaving a weak spot that gives slightly.

 

I will do as you suggest and cut the membrane to see what lurks below. Was this a usual method of construction 20 years ago?