Plain and over­lap­ping (me­chan­i­cal) tiles

French Property News - - Expert Advice -

So-called ‘plain’ tiles are much smaller than canal tiles; they are rec­tan­gu­lar and ef­fec­tively flat, but have nibs un­der­neath and are usu­ally pro­vided with nail holes so that they can be hooked over and nailed to tim­ber bat­tens. Tra­di­tional hand­made plain clay tiles are still used through­out many parts of France.

Over­lap­ping (or ‘me­chan­i­cal’) tiles al­most al­ways have nibs un­der­neath. They can be flat or ribbed and are man­u­fac­tured to a pro­file such that they over­lap or in­ter­lock with each other on their longer, in­clined, edges and usu­ally on their hor­i­zon­tal edges as well; this is in­tended to hold the tiles in place and to pre­vent rain from get­ting blown un­der­neath them.

The main prob­lems with plain or over­lap­ping clay tiles are crack­ing and break­ing, as a re­sult of very high or very low tem­per­a­tures. An­other is­sue is ‘de­lam­i­na­tion’, which is where the sur­face grad­u­ally flakes away over the years – gen­er­ally ex­ac­er­bated by frost dam­age – un­til the tiles be­come por­ous.

It is usu­ally pos­si­ble to re­place bro­ken tiles on an in­di­vid­ual ba­sis but when de­lam­i­na­tion oc­curs it is of­ten found to be wide­spread, par­tic­u­larly in the case of the thin in­ter­lock­ing type clay tiles that were used ex­ten­sively about 60-70 years ago. So if this hap­pens the en­tire roof cov­er­ing might then need to be re­newed.

A closer look

If you’re buy­ing a house with a tiled roof I sug­gest you have the roof sur­faces closely ex­am­ined, ideally be­fore mak­ing the pur­chase. It might be fea­si­ble to do this ei­ther your­self or with pro­fes­sional as­sis­tance from ground level, us­ing binoc­u­lars, but if the roof has a low pitch and you can’t get far enough away to see it you might need to em­ploy a con­trac­tor to get onto the roof us­ing long lad­ders.

If it looks as though the roof is sag­ging, the struc­ture it­self may be at fault. Many older struc­tures were not built to to­day’s stan­dards and ex­ces­sive de­flec­tion in the tim­bers can oc­cur with age. This prob­lem can arise if an old roof cov­er­ing is re­newed with heav­ier ma­te­ri­als (slates be­ing re­placed with con­crete tiles, for ex­am­ple); if you’re think­ing of chang­ing the roof cov­er­ing with a dif­fer­ent kind of ma­te­rial you should first have the struc­ture it­self checked.

It may well be pos­si­ble to build in ad­di­tional tim­bers to strengthen an oth­er­wise weak or in­ad­e­quate roof struc­ture, but ad­vice on this should be ob­tained from a prop­erly qual­i­fied pro­fes­sional to en­sure that al­ter­ations to the struc­ture do not trans­fer the weight in­cor­rectly.

A solid frame­work

Whereas pitched roofs have tra­di­tion­ally been built with a tim­ber frame­work, there was a pe­riod some 40-50 years ago when steel trusses were in­cor­po­rated, or the struc­ture of pitched roofs was built wholly of steel mem­bers or con­crete, par­tic­u­larly in areas of France where ter­mites were a po­ten­tial prob­lem.

Flat roofs can be built wholly of tim­ber, with a deck of tim­ber board­ing or, say, ply­wood pan­els over tim­ber joists or beams, or steel or con­crete beams can be in­cor­po­rated. Al­ter­na­tively the struc­ture can be all con­crete, per­haps us­ing pre­fab­ri­cated sec­tions that are sim­ply dropped into place and cov­ered with a thin ce­ment screed.

A form of con­struc­tion for flat roofs, ter­races and in­ter­nal floors, of­ten found in French houses built 80-100 years ago, con­sists of steel beams typ­i­cally spaced 500mm apart with vaulted/arched ma­sonry of bricks or hol­low clay blocks ( briques) in be­tween, sup­port­ing a thick­ness of con­crete above. It is un­for­tu­nate that in this kind of con­struc­tion the con­crete fin­ish was mostly con­sid­ered to be suf­fi­ciently dense, and it was not stan­dard prac­tice to pro­vide a weath­er­proof fin­ish. But over time, mois­ture can pen­e­trate the con­crete due to fine cracks or sim­ply age. The prob­lems I have com­monly found are that the steel beams have cor­roded, and the brick arches in be­tween have dis­in­te­grated. Ob­vi­ously you need to be able to get un­der­neath the struc­ture to check for dam­age of this kind.

Some­times it is fea­si­ble to pro­vide a new weath­er­proof sur­face and sim­ply clean up or re­in­state the sup­port­ing struc­ture, but other times the de­te­ri­o­ra­tion is so bad that I have to rec­om­mend com­plete or par­tial re­newal of this kind of con­struc­tion.

A sim­i­lar sit­u­a­tion fre­quently arises in the case of older flat roofs and ter­races made of re­in­forced con­crete where, due to a poor or non-ex­is­tent weath­er­proof fin­ish, mois­ture has pen­e­trated the struc­ture over the years such that the re­in­forc­ing steel in­side has cor­roded and caused the rel­a­tively thin layer of con­crete be­tween the steel and the sur­face un­der­neath to crack or even break away.

Older flat roofs that are not in­tended to be used as ter­races may be cov­ered with lead or zinc sheets. The best kind of sur­face for a flat roof is in­vari­ably as­phalt, but it is ex­pen­sive and nor­mally found only on com­mer­cial build­ings. Do­mes­tic flat roofs are usu­ally cov­ered with roofing felt or mod­ern high-per­for­mance mem­branes that are made al­most en­tirely of syn­thetic ma­te­ri­als.

If a flat roof is to be used as an out­door ter­race it ought to be cov­ered with tiles of some kind to pro­tect the weath­er­proof sur­face un­der­neath it. Flat roofs are not in­tended to be com­pletely flat but should have a gra­di­ent (ideally not less than 1 in 60) slop­ing to­wards one or more rain­wa­ter out­lets. Prob­lems can arise where flat roofs have in­ad­e­quate gra­di­ents. Un­for­tu­nately, it is usu­ally a com­pli­cated and ex­pen­sive job to im­prove the gra­di­ent of an ex­ist­ing flat roof.

If leaks oc­cur in a flat roof you should check the con­di­tion of the ‘deck’ to which the roof cov­er­ing is fixed be­fore sim­ply re­pair­ing or re­new­ing the roof cov­er­ing. Wood chip­board and certain other types of pan­els used for roof decks can be per­ma­nently dam­aged, and will not re­gain their orig­i­nal strength once they have be­come sat­u­rated.

Sad to say flat roofs in the drier parts of France are of­ten con­structed to a stan­dard found to be lack­ing when a good down­pour oc­curs so be warned!


All roofs that contain in­su­la­tion should be ad­e­quately ven­ti­lated – some­thing which is fre­quently over­looked when in­su­la­tion is in­stalled in a pre­vi­ously un­ven­ti­lated roof. Un­ven­ti­lated roofs can at­tract con­den­sa­tion, and this can have a harm­ful effect, par­tic­u­larly in roofs of tim­ber con­struc­tion.

Left: These me­chan­i­cal (in­ter­lock­ing) tiles are prob­a­bly get­ting on for 80 years old and will soon need to be re­newed on a piece­meal ba­sis or in their en­tirety

Right: The un­der­side of a flat roof formed with vaulted brick­work be­tween small sec­tion steel joists. Wa­ter pen­e­tra­tion over the years has caused the com­po­nents to de­te­ri­o­rate

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