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Friday 27 May 2011

Concrete Floors

So here we are again, with some more super action shots of concrete! The decision was made to use a pre-cast concrete floor in these houses for a variety of reasons including,
The extremely good sound resistance of concrete floors both impact and airborne and allows the use of concrete partition walls at first floor.

The external walls and internal partition walls where taken up to chamber level and the floor is craned into place,


The concrete planks have been designed and produced specifically for this site and are laid onto the 190mm thick external wall ensuring that there will be enough room to construct a 100mm block wall which will act as a shutter for the concrete.





Once the 100mm course of thin joint blockwork has been installed a wooden shutter is constructed around the stairwelland as seen here the floors are kept separate at the party wall junction. As there is no Robust Detail for a solid party wall used with a solid concrete floor each dwelling will require pre-completion testing.


Additional steel has been designed for this floor and installed as shown. One important aspect of a Passive House is the ventilation system, this project has a Mechanical Ventilation with Heat recovery system and the ducting will be hidden within the concrete floor. 




Concrete is pumped into place and is power floated to produce a smooth hard wearing finish which is ready to accept the required floor covering.

Monday 21 February 2011

External Walls

Here we are after a slight delay, back on site. The external walls are now up to chamber, pictures here show the 190mm external walls being constructed from a new aircrete block with a thermal conductivity of 0.07W/mK and have a bed tolerance of just ±1mm which allows, as you can see, Clan Thinset mortar to be used to create a mortar joint of just 2mm.
When using Clan Thinset mortar the blocks are bonded together to produce a homogeneous aircrete wall, you can see a red mesh on one of the joints. This is Clanmesh which is a glass fibre fabric which has been specially designed and tested for use in Thinjoint mortar. Clanmesh distributes any stresses which may build up in the wall.
 
This method of construction produces a virtually airtight wall which will not require a membrane to achieve the 0.6 SCH air (changes per hour) required by the Passiv Haus Institute.

The party wall on this pair of semis is being constructed from a dense concrete block wall laid with Thinjoint mortar. This is not normally possible because the tolerance on the bed faces is not good enough to achieve the 2mm joint. However, when the blocks are laid on their side the bed face becomes the parallel side formed from the mould side when the blocks are manufactured. This method of build overcomes the problem of creating an airtight party wall, a thermally efficient party wall and achieving a sound test of of 60Db.



Tuesday 4 January 2011

First Course of Blockwork

The first course of blockwork is laid onto the reinforced concrete slab. A DPC is placed adjacent to the perimeter insulation which is formed by the upstand of the sub-foundation insulation.



























 This first course is laid on a bed of sand and cement mortar to level out any imperfections in the raft. The vertical joints are bonded with Thinset mortar to ensure the bond is kept in subsequent courses and also adds a little rigidity to the blockwork.






The blocks are manufactured from a material which would normally go to landfill, this is added to a little cement to act as a binder and aluminium which expands in the mix to produce a concrete block with millions of air bubbles. This process is not unique but we have found a way of producing the block to give the best thermal value of any aircrete block on the market with a thermal conductivity of 0.07W/mK almost 35% better than the standard 0.11W/mK.


The 190 wide blocks are laid with Thinset mortar whichbonds the blocks together with a 2mm joint. This is possible because the blocks are manufactured to a tolerance of ±1mm. The mortar is applied with a notched trowel which delivers a pre-determined amount of mortar to the block. This allows a fast but more importantly precise method of building, minimising thermal bridging and ensuring airtightness as the wall is built.