Cavity Construction

(Explaining the Hitex Diamond Cavity – Patent Pending)

Building Industry Experience Shows

	Without a cavity the building can sweat and rot.
	Everyone is talking battens but that’s only politics.
	No-one knows how to install a batten cavity system.
	No-one wants to pay for battens – or install them.
	Everyone is playing follow the leader – what choice do they have?
	But will a batten cavity work?

Background

Untreated timber has shocked the industry regulators.  Now it is time for change.  But is reverting back to treated timber enough?  For some claddings like EIFS it probably is, unless there is a sustained leak.

A building must be able to breathe to dry out.  But how much breatheablity is necessary?

Testing

Hitex recently conducted testing of its new Diamond Cavity system.  It drained water in the water loading test (unreported).  But more importantly it actually dried wet timber in the drying test.  See Hitex Research Bulletins 301-307

D150 and D ALL are both examples of the Hitex Diamond Cavity system.

Graphs for Hitex Drying Project

Cavity Design

The Diamond Cavity satisfies the Hunn Report recommendations.  That is “provide a second line of defence …… and a means of drying out any wet element”.  By being able to dry out a wall, the Diamond Cavity system is fit for purpose.  No more encapsulated framing sweating and rotting.

NB: The leak must first be stopped before the wall can dry out.

Cavity Objectives

The objective of the Hitex Diamond Cavity is to provide a space between the cladding and building wrap that serves to:-

1. Keep the building wrap away from the EIFS to eliminate bulges preventing the cavity from operating.

2. Designed elements within the Hitex allowing free drainage to baselines or flashings (2 storey or more).

3. Will not affect the R-value.

4. Allows adequate support for the Hitex

   1. so it does not deform or lose its intended shape

   2. so it maintains its wind loading resistance

5. The depth of the Diamond Cavity is commensurate to its

   1. water loading expectancy of building type

   2. drying potential claimed by Hitex

6. Has no horizontal bars that can store water or prevent the movement of vapour

7. Where ventilation is provided the thermal difference can be compensated for by increased thickness of polystyrene.

8. The Diamond Cavities are interconnecting to allow vapour re-distribution around the walls.

9. Prevents vermin entry.

10. Restricts wind driven moisture entry unless in extreme circumstances.

11. The Diamond Cavity materials resist water absorption.

12. Prevents damp air ventilating into roof or mid floor voids.

13. Has a minimum opening at the baseline to allow for cyclical vapour diffusion as wood emc changes during the year.

14. Building paper to have a vapour permeability of not less than 1 grm/hr/m².  Hitex recommend frameguard or bitumen building paper.

15. Where building is to be air-conditioned these cavity conditions do not apply.  Separate HVAC engineering is required.

16. The maximum thickness of Diamond Cavity system shall not be more than 100mm for fire and anchoring reasons.

Where the Diamond Cavity is installed over solid backing boards the designer shall ensure no internal gutters, water pipes, parapets or decks are included at the same location – in case these leak into the framing. 

The Hitex Diamond Cavity satisfies all these requirements.

Hitex Diamond Cavity

The Hitex Diamond Cavity system with a cavity depth of 10mm is adequate for most constructions.  For lesser loading walls e.g single storey buildings where leaks are likely to be of a less harsher nature and for HVAC designs, thinner 6mm depth Diamonds can be manufactured. 

Diffusion at Work                                   Detail showing Diamond Cavity

Page last updated Tuesday, 08 March 2005