The Renegade Conservatory Guy who is a respected in the industry for his views, has recently taken interest in my cavity tray and vertical dpc articles and has asked the same basic questions to some of his readers, whether to fit them or not and is there a difference between the sales guys and the technical guys in their views on this issue? (Link to his article at bottom of page) I would like to thank him for his interest and his reader’s views, which range from quite sensible approaches to some that I found comical in content and humour.

In light of such diverse opinions I have decided to publish some more technical information which may or may not, help those who are unsure on the decision they need to make on guaranteeing a waterproof conservatory. (My original article links below)

Do you sell, survey and install cavity trays on Conservatories ? If you don’t sooner or later it will cost you.

Do all Conservatory and Orangery surveyors specify vertical dpc’s against the house walls on Conservatory and Orangery Installations

After many years surveying and managing installations across a very broad area of the country, I can categorically tell you if the house is face brick cavity construction, the only way you can guarantee 100% waterproof integrity of the conservatory is to fit cavity trays. If you don’t then the water ingress is always going to be a roll of the dice. “Some people may have rolled lucky sixes years, but you won’t keep winning on the roll of a dice forever”

It appears there are very varied opinions on whether or not cavity trays and vertical dpc’s are required in certain areas of the country or not. Some offer them as part of the sale. Some opinions are purely based on cost of sale. Some have said, they have never had a single leak in thousands of installations fitted without cavity trays, or vertical dpc’s. Then there were those who stated that they have installed in the Scottish Highlands and had no problems. Others will insist that their areas are classed as “sheltered areas”.

To clarify this point I have published a map that shows areas of wind driven rain and it appears to show only a very small proportion  of the UK as being a “sheltered area”

And for those of you installing in Scottish Highlands see below taken from “The Scottish building standards technical handbook for conservatories” This published handbook has a very good guideline to all the correct construction methods of any conservatory, irrespective of whether or not it requires building regulations or not, and some could learn a thing or two by reading it through.

Surely it would make sense to follow professional advice, fully protecting the customer’s investment.

I struggled to see any sheltered areas on Scottish weather exposure map at all and the majority of the map showed “severe or very severe” exposure zones.

The Scottish building standards technical handbook for conservatories, link for pdf download below



Again, just to ensure that nobody is trying to specifically promote their vested interests in cavity tray sales, I have randomly picked another cavity tray company and copied their technical advice.

A very useful technical information site for construction I have used is “The faculty of Built Environment” and again there is a lot of very useful building information which may help you in your decisions on all aspects of conservatory construction.

I understand that the area of the country where I live is classed as a severe area for weather, and from my experience most companies in that area take the cavity tray installation into consideration, and all of the companies I have ever worked for small and national in my area sell, survey and install them, or get a legally binding disclaimer written in to the contract (as shown in previous article on cavity trays)

Another interesting definition of a cavity wall

A cavity wall is designed to prevent moisture penetrating to the inside face of the wall and causing damp problems in the building.

In many situations it is necessary to include cavity trays in the wall, to prevent water penetration to the inner leaf.

This occurs mainly:

– where the cavity is bridged, eg by lintels above door and window openings, over air bricks, ducting, meter boxes etc

– where an external wall becomes an internal wall at a lower level, eg pitched or flat roof abutments, parapet walls.

What I still can’t understand is how some people say “they never fit cavity trays or vertical dpc’s and have never had a single instance of water ingress when turning an existing external wall into an internal wall” even in most exposed areas of the UK.

All the technical bodies point to fitting water ingress barriers, in cavity walls on conservatories and people ask the question below, click on the link and read for yourself


Are cavity trays and vertical DPCs overkill?

What it appears to boil down to at the end of the day is :-

”The decision on whether to roll the dice or not is down to the individual company”

  1. Martyn Hamer says:


    All good information! I think you,ve coverd our side of the disscussion very well.
    The only thing I,d add is for water ingress to occur via the cavity wind driven rain isnt always needed. Persistant rain can and will saturate a wall to completion and bridge any flashing threshold if the rain is of the type we,ve had these last few years, being constant and not allowing for any drying of the already soaked masonry,
    You only need to pop your head in the loft on most properties to see salting of the previous dampness around the chimney breast area, newer properties usualy build a Lead tray in the stack above the finished roof level, however older properties are particulary prone to this showing how once saturation point has been reached the dampness will bridge the lead flashings and soakers.
    I,m sure theres plenty of roofing contractors who will vouch for this problem.

    • Steve Williams says:

      Hi Martyn,

      Again thanks for your comments,

      I took it for granted that people would naturally understand that that persistent rain would be detrimental to internal walls not being protected by water ingress barriers, but thanks for making it clearer.

      Funnily enough I was carrying out a loft conversion on my bungalow a few years ago and saw salt deposits on the chimney in the attic. It wasn’t long before the damp appeared on my kitchen ceiling. It’s still there now, I need the stack taken down to roof level and rebuilt and a liner put in as the whole stack is splitting as well.


  2. Martyn Hamer says:


    Depending on what the stack is serving check out flue stox at salfold I think they are on the web, they specialise in anything flue wise, gas, oil, solid fuel, we,ve taken dozens of stacks down that were soaking and fitted a compliant pipe/flashing/cowl curing the dampness once and for all.
    Bungalows are particulary bad as theres usualy less area left to dry out in the loft before the ciieling is reached. Unless the stack is a feature of the property its sometimes far more cost effective to remove it and fit the pipe, all the parts are usualy stainless steel and corgi, hertas etc aproved

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