round double seal manhole cover?

[DIYedboy]

I am building an extension which will mean that the new manhole will be underneath a suspended timber floor. The new manhole will be one of those circular plastic jobs BUT I can't find a circular (450mm) double seal cover that will fit into the raiser rings............is there such a thing?

 

[freddiemercurystwin]

What's the point of having a manhole under a floor? Or is the void big?

 

[Newboy]

Those "circular plastic jobs" are designed for external installation - you wont find a double seal cover to fit.

Second FMT comments - why have a manhole under the floor?

 

[DIYedboy]

The floor will be suspended timber, surely therefore the manhole cover will finish 6" beneath the chipboard floor and level with the oversight concrete.

The drain crosses the boundary into nextdoor therefore the manhole position is fixed as my extension goes to the boundary

 

[Newboy]

Is the drain serving more than just your house? Does it come from your neighbours to you and then onto your other neighbour for example.

There is no point in having a drain cover 6 inches below a suspended timber floor - how would you access it in the event of a blockage?

 

[DIYedboy]

it starts at my house, runs beneath the extension turns 90 degrees and crosses into the neighbour. When the floor is screwed down, you make an access panel which can be lifted up in order to get to the cover. The room above is going to be a utility room.

 

[Newboy]

Bring the chamber up to FFL and fit a double seal screw down cover.

If you fit a standard cover into the void, the first time that you'll know you've got a blockage is when the void is full of effluent.

 

[DIYedboy]

Thanks NEWB I definitely don't want the cover getting lifted up, so a screwdown job is a good idea, but it would be a lot simpler to leave it just beneath FFL so there's no fiddlin about trying to get the height just right.

 

[chappers]

you can get a square topped double sealed cover to fit a round riser, personally I would get another riser ring or two and bring it up flush with the floor

 

[noseall]

We just haunch a lump of concrete around the chamber perimeter and re-hash the top with masonry, re-shaping if necessary. Rarely does a chamber section finish where you want it to in terms of height.