Passive House cavity wall construction

The passive house pharmacy and apartment building is beginning to take shape! Since I last reported the precast concrete floor slabs have arrived and external cavity wall construction has started. This is my first masonry passivhaus so there is a learning curve for me on how to build a robust super-insulated masonry wall. I will share with you on this site the research and implementation of all I have learned about this very cost-effective way of building to the passivhaus standard. Cavity widths for this project are 250mm typically and will be filled with graphite-enhanced bonded expanded polystyrene insulation beads.

One of the main concerns with cavity wall construction is the mortar droppings from the laying of the blocks accumulating at the bottom of the cavity and on the wall ties bridging the cavity below. Block layers are supposed to use a cavity board to catch these. Block-layers apparently don’t like doing this because it calls into question their ability and slows them down. Those days are over guys – change practices or get out of the business!! With new Building Control Regulations this year inspection is going to become a lot more real!

My approach was to ask the contractor to leave out blocks at the bottom of the cavity for inspection/cleaning which O’Gorman Construction had no problem in doing. The result was perfectly clean cavity bottoms, no mortar on wall ties and clean inner faces of cavities. Take a look!!

You will notice a difference in the blockwork above and below the DPM line. The lower block is lightweight Quinnlite Aerated Concrete block which has a low thermal conductivity to eliminate a traditional thermal bridge at the foundation. The upper blocks contain GGBS low-carbon cement as previously reported.


Detailing of masonry cavity wall passive house foundation

See attached explanation detail of my typical foundation. You will note tanking as the ground level is lower than external in places. Also note shadow gap plaster detail in lieu of skirting boards (wall must be parged before plaster bead applied) and tapered insulation to perimeter of concrete floor slab as this will be exposed. These details would be much simpler in domestic conventional construction so don’t let it put you off! See Thermal Bridge analysis image showing temperature calculation at coldest point for the existing party wall detail. This calculation assumes -10 degrees C external temperature!

With wall rising and floor slabs in, we begin to appreciate the sense of space which the new pharmacy will enjoy.



Please note; details published in this site are project specific only and no liability shall attach to their use by third parties without consultation and permission by Paul McNally architect.