Tiled roofs air permeability: experimental and numerical investigation

The construction sector accounts for more than one-third of the global energy consumption. Ventilated roofs and facades are among the adopted strategies to improve the efficiency of the building envelope: air flowing in cavities under the cladding layer, in fact, is particularly effective in hot summers for the reduction of the incoming heat flow due to solar radiation. Regarding roofs, satisfying results were obtained through the realization of a 5-10 cm air gap under the covering layer which allows better thermal performances of the roof and a reduction of the energy consumption for air conditioning. Although most of products and techniques applied are based on the assumption that air enters only from the eaves line and exits at the ridge one, it is demonstrated that in case of discontinuous mantles, a great contribution derives from air entering from the overlaps. As a matter of fact, air entering from the eaves line is strictly dependent on the wind direction and benefits are evident only when the wind is perpendicular. In all the other cases, buoyancy forces due to air heating under the mantle cannot provide such a consistent contribution. Tiles overlaps’ air permeability allows the wind to enter from multiple directions with consequent greater ventilation of the substrate. Experimental research regarding the performances of pitched tiled roofs was conducted at the TekneHub laboratory of the University of Ferrara and the results are here presented. The tests carried out aimed at investigating the behaviour of different configurations of tiled roofs both from a thermal and an energetic point of view. Three configurations were compared: one was a completely sealed roof (sealed), one had sealed eaves and ridge lines but unsealed tiles overlaps (laid) and the last one was a ventilated roof (vented). The comparison between the sealed and the ventilated roof confirmed the improvement of the performances when in presence of an air cavity. The ventilated roof was then compared to the laid roof to assess the actual contribution of the air permeability of the tiles, and results clearly showed a great contribution, even in case of low wind.


Introduction
The e vir e ta i pact is a g the st discussed issues especia y i bui di g a d c structi sect r which acc u ts f r re tha e third f the g ba e ergy c su pti s 1 With a ever cha gi g ife sty e a d a ways higher ivi g sta dards e ergy c su pti re ated t bui di gs is c ti u us y i creasi g H wever the bui di g's e ergy de a d is strict y c ected t the efficie cy f its e ve pe 2 "a y are the app icab e tech gies t c up e i d r c f rt a d reduced e vir e ta i pact b th ew bui di gs as we as existi g es a g which there is the ad pti f ve ti ated surfaces Ve ti ated r fs are particu ar y effective i h t c i ates such as the "editerra ea e as they a w a reducti f the i c i g heat f ux i su er 3 a d creati g a i su ati g ayer f air ar u d the bui di g's i er she i wi ter 4 'atura ve ti ati gai ed re a d re atte ti as a p te tia tech gy f r i i i(i g e ergy c su pti suitab e f r a th se c texts characteri(ed by heights restricti s r refurbish e t i itati s 5 Preve ti g the heat tra sfer thr ugh the bui di g e ve pe i stead f c i g the bui di g fr the pe etrated heat is effective t y fr the e vir e ta p i t f view as reduces the c i g p wer c su pti but a s fr the ec ic e c cer i g the i itia i vest e t as we as the ife cyc e expe se 6 The efficacy f ve ti ated r fs was assessed by ea s f ab rat ry tests 7 8 as we as fu sca e de s Eve th ugh it is sti freque t y assessed that air e ters fr the eaves i e a d eaves at the ridge e it is de strated that i case f disc ti u us a t es (i e c ay ti es) air e ters a d eaves eve fr the ti es' ver appi g thus e ha ci g the ve ti ati u der the c addi g ayer i the s ca ed Ab ve Sheathi g Ve ti ati (ASV) pr vidi g a additi a etw r4 f airf w paths 9 10 I this paper the resu ts f a experi e ta research the perf r a ces f differe t c figurati s f r f with f cus a t e's air per eabi ity are prese ted

Methodology
The research here pr p sed is based experi e ta tests carried ut duri g su er t eva uate the effect f the air per eabi ity a ti ted r f c vered by sta dard P rtuguese c ay ti es Exp iti g the experie ce gai ed i previ us researches 8 10 11 the c ected data are ea t t be used t ca ibrate a u erica de with the s ftware C9"S9: "u tiphysics which ai wi be the i p e e tati f a equiva e t r f ade f a p r us ediu ab e t si u ate the behavi ur f a ti ed ve ti ated r f with a si p ified ge etry theref re reduci g the si u ati g ti es The experi e ta tests were carried ut at the Te4 eHub :ab rat ry f the U iversity f Ferrara i a experi e ta bui di g ( c4 up Figure 1) which was rea i(ed f r the Eur pea pr =ect :IFE C i ate Cha ge Adaptati HER9TI:E (High E ergy savi gs i bui di g c i g by R9 f TI:Es shape pti i(ati t ward a better ab ve sheathi g ve ti ati ) The bui di g with a recta gu ar 10 x 8 p a is ade f five ad=ace t i depe de t test r s a d tw guard r s the sides that e sure the sa e c diti s i a the test r s The te perature i each r was 4ept c tr ed by ea s f a digita ther stat that regu ated a fa c i The r f is ti ted with tw sy etrica pitches i c i ed by 20? a d rth s uth rie ted " re ver i rder t av id a y i terfere ce fr the surr u di g that ay affect the perf r a ces the c4 up was bui t a e ba 4 e t ab ut 2 ab ve the gr u d eve The stee structure bui di g was c ad with sa dwich pa e s b th f r the peri eter wa s as we as f r the i ter a es whi e as regards the r f a w de dec4 c vered by a waterpr f p y efi e bra e was arra ged as supp rt f r each c figurati i vestigated    I the fra e f a wider research the perf r a ces f differe t r fs c vered with sta dard P rtuguese c ay ti es were it red i rder t assess the effective ess f the air per eabi ity f a disc ti u us a t e A pre i i ary test was carried ut by c pari g the perf r a ces f a ve ti ated r f ( Figure 2) with a c p ete y sea ed e ( Figure 3) The f r er had a sta dard w de batte a d c u ter batte structure that shaped a 4@3 air cavity with expa ded eta the eaves i e the atter had ti es direct y p siti ed the dec4 with supp rt eaves a d ridge i es sea ed with p yuretha e f a a d ti es' ver aps c sed by ea s f a waterpr f adhesive tape The resu ts btai ed were used as be ch ar4s f r the subseque t test i which the actua c tributi f the air per eabi ity f the a t e was i vestigated by c pari g the sa e r fs as the previ us test but with the waterpr f adhesive tape re ved fr the ti es' ver aps I this ast c figurati ti es were direct y p siti ed the dec4 with sea a t the ver aps a d the eaves a d ridge i es were 4ept c p ete y c sedA air c u d e ter r eave the ASV y thr ugh the ver aps ( Figure  4) This c figurati was c ve ti a y ca ed aid

Monitoring system and data acquisition
Severa se s rs were i sta ed f r the it ri g activity F r what c cer s the b u dary c diti s a weather stati utside the ab rat ry c ected data ab ut s ar radiati air te perature a d hu idity wi d speed a d directi with a ti e step f 15 i utes Additi a se s rs were i sta ed f r re accurate easuresA a i c i ed pyra eter para e t the r f s uth pitch was i sta ed ab ve the c4 up r f t easure the s ar radiati a RTD Pt100 was i sta ed right utside the rth wa f the c4 up t easure the air te perature a d f ur cup a e eters were p siti ed at differe t heights (1 50 -2 50 -4 00 -6 00 ) t esti ate the wi d pr fi e Regardi g each test r a accurate it ri g syste was arra ged a d se s rs were i sta ed i differe t p siti s f the pitches as we as betwee the ayers 9 b th the rth a d the s uth pitch te perature se s rs a d a e eters were i sta ed As regards te peratures T type ther c up es (accuracyA 0 5 D) easured the te perature f the ti e i trad s (Ti e te perature Tt) whi e RTDs Pt100 (accuracyA 0 5 D) easured the te perature f the air i the cavity (ASV te perature Ta) the te perature f the extrad s a d i trad s f the w de dec4 (Dec4 te perature a d Cei i g te perature respective y) a d i side the r (R te perature Tr) As regards a e eter severa h t wire a d h t fi s a e eters (accuracyA 0 05 Es) were p siti ed at differe t secti s f the pitches i the air cavity t easure the ve city I additi a heat f ux eter (u certai ty f ca ibrati A 3%) was p siti ed i the ce ter f each s uth pitch the i er side f the w de dec4 (HF) t qua tify the heat f ux e teri g fr the r f I Figure 5 a ax etric view f e f the r s a d a detai f the se s rs' p siti a d e c ature are depicted A the ab ve e ti ed se s rs were c ected t a data gger (DataTa4er DT85 series 4) which acquired data with a ti e step f e i ute a d saved the every 30 i utes i a c ected c puter i csv f r at :ast y ther a e ergy eters were i sta ed each fa c i t it r the e ergy require e t f r c i g f each r a d thr ugh a " bus gateway were c ected t the sa e c puter as the data gger with a ti e step f 5 i utes

Results and discussion
As the tests were t carried ut at the sa e ti e tw si i ar peri ds f three c secutive days were se ected i ter s f air te perature s ar radiati wi d speed a d directi a d resu ts are hereafter prese ted

Vented (V) vs Sealed (S) roof
As depicted i Figure 6 a d Figure 7 duri g the se ected peri d f the first test (August 2019) the air te perature f uctuated betwee 20 ?C at ight a d 34 ?C duri g the day with a s ar radiati that reached pea4s f ear y 950 WE 2 The average wi d speed was f ab ut 1 Es with pea4s f 1 5 Es i the first day a d directi s were ai y east a d s uth east with pea4s fr west A g the severa se s rs used th se p siti ed i the idd e f the s uth pitch (depicted i Figure 4) were c sidered as the st represe tative f the average behavi ur f the r f I Figure 8 are depicted the te perature f the ti e (Tt) a d the te perature a d ve city f the air i the ASV (Ta Va) whi e i Figure 9 are depicted   the first day f the se ected peri d Give that the i c i g heat f ux f the sea ed r f reached pea4s betwee 40 WE 2 a d 50 WE 2 the reducti rec rded i the ve ti ated r f was f ab ut 20% As regards the air ve city i the ASV i Figure 8 the hist rica series f the c ected data is depicted As expected u der the sea ed r f air was c p ete y sti whi e u der the ve ti ated e air was vi g a th ugh the registered va ues were very w a d at the i it f the se s rs' precisi This h wever is due t the w wi d speed that characteri(ed the peri d here c sidered I Figure 10 the va ues were the c assified acc rdi g t the wi d directi If air e tered y fr the eaves i e higher ve city i the ASV w u d be expected with wi d fr the s uth 9 the c trary fr the c ected data wi d directi see s t be t very re eva t a d f r each directi a reducti fact r betwee 0 1 a d 0 2 is ticed " re specifica y with wi d directi s betwee 45? a d 135? ( rth east t s uth east) the reducti fact r is s ight y higher a d ar u d 0 2 whi e i case f wi d directi s betwee 180? a d 360? the reducti fact r is ar u d 0 1 C sideri g the rie tati f the c4 up the ver aps betwee ad=ace t ti es face east theref re the higher reducti fact r ca be due t the greater ease f air t e ter :ast y s e c siderati s were d e f r what c cer s the e ergy require e t f r c i g I Figure 11 are depicted i detai the r te perature a d the e ergy required f r c i g f r e f the days f the se ected peri d re specifica y the sec d e The f uctuati s i the r te perature are due t the switchi g a d ff f the fa c i s I the r u der the sea ed r f the fa c i was switched by the digita ther stat 22 ti es whi e i case f the ve ti ated r f it happe ed 19 ti es A a ysi g the data c ected by the ther a e ergy eters the e ergy required t ai tai the set p i t te perature with the sea ed r f was f ear y 394 WhE 2 whi e with the ve ti ated e it was f 330 WhE 2 Theref re the reducti i the e ergy require e t is f ab ut 16%

Vented (V) vs Laid (L) roof
As ab ve e ti ed after havi g c pared the ve ti ated t the sea ed r f the sea a t the ti es' ver aps was re ved I this third c figurati a ed aid (:) ti es were direct y p siti ed the w de dec4 a d the eaves a d the ridge i es were sea ed with p yuretha e f a As the previ us test a peri d f three c secutive days (August 2019) was se ected a d the b u dary c diti s are depicted i Figure 12 a d Figure 13 The air te perature was s ight y higher tha the first test a d f uctuated betwee 23 ?C at ight a d 36 ?C duri g the day whi e the s ar radiati was quite si i ar a d reached pea4s f 950 1000 WE 2 The average wi d speed was s ight y wer tha 1 Es with pea4s f 1 6 Es the sec d day a d the directi was ai y s uth east with pea4s fr west I Figure 14 are depicted the te perature f the ti e a d the te perature a d ve city f the air i the ASV whi e i Figure 15 the r te perature a d the heat f ux thr ugh the r f As depicted the r set p i t te perature was the sa e f the first test that was 26 ?C I this case the differe ces betwee the tw c figurati s decreased Duri g the h ttest h urs i the aid r f the te perature f the ti e reached pea4s f 57 58 ?C i the first a d sec d day a d f ear y 53 ?C i the third e whi e i the ve ti ated r f the te perature f the ti e was Figure 11. Test 2. Air temperature and solar radiation. s ight y wer the first tw days a d ear y 3 D higher the third day As regards the te perature f the air i the ASV i the ve ti ated r f the va ues reached pea4s f ear y 47 ?C each f the se ected days 9 the first a d sec d day the te perature i the aid r f was ab ut 5 5 D higher whi e i the third day the differe ce was f 3 D 9 average the pea4s differe ce reached c rresp ds t a reducti f the te perature f the air i the ASV i the ve ti ated r f f ear y 10% As regards the heat f ux the pea4s reached i the ve ti ated r f were betwee 40 WE 2 a d 45 WE 2 whi e i the aid e the pea4s were s ight y higher with differe ces up t 6 WE 2 the first a d the sec d day a d f 3 WE 2 the third e 9 average the pea4 reducti f the i c i g heat f ux i the ve ti ated r f was f 10% C cer i g the air ve city i the ASV i Figure 14 is depicted the hist rica series f the c ected data Air u der the aid r f was vi g but as f r the previ us test the wi d speed was quite w (a c c diti i Ferrara) a d s the va ues f r the air ve city i the ASV were at the i it f the se s rs' precisi I Figure 16 these va ues were c assified acc rdi g t the wi d directi C pared t the first test i which the wi d speed was quite h ge e us fr a the directi s duri g the three days se ected f r the sec d test the

Extension of the results
I the ab ve rep rted data c ear evide ce f the c tributi f the ti es' per eabi ity e erges The differe ces betwee the three rea i(ed c figurati s are evide t i the h ttest h urs f the day whi e with w s ar radiati a d air te perature the behavi urs f the r fs are a st ide tica F r this reas a better detai ed c paris was ade betwee the three r fs c sideri g a ger peri d tha the previ us es but se ecti g days with c parab e b u dary c diti s a d a a ysi g data y i the i terva 12A00 15A00 As the c4 up e ve pe had very w i ertia the se ected ti e i terva was exhaustive t c sider the peri d i which the exter a c diti s were re critic a d the e ergy require e t was greater I Tab e 1 are depicted the average va ues f r s ar radiati  air te perature a d  wi d speed f r b th the peri dsA peri d 1 a d peri d 2 are the exte si s f test 1 a d test 2  respective y The average air te perature i the first peri d was f ear y 33 ?C whi e i sec d e it was s ight y higher a d ab ut 33 5 ?C The s ar ad was a st the sa e a d ar u d 800 WE 2 as regards the wi d speed i the first peri d the average was f 0 9 Es a d i the sec d e it was f 1 3 Es  Figure 18 the average va ues i ter s f ti e te perature air i the ASV te perature heat f ux a d e ergy f r c i g are depicted divided acc rdi g t the it ri g peri d C pari g the ve ti ated a d the sea ed r f great reducti due t the air f wi g are visib e The average te perature f the i trad s f the ti e was 3 D wer equa t 5 6% whi e as regards the air i the ASV the differe ce was uch greater as it was f 8 3 D c rresp di g t a reducti f 16 2% C cer i g the i c i g heat f ux the differe ce betwee the average va ues was f ear y 10 WE 2 c rresp di g t 21 6% a d this was the ref ected t the e ergy required f r c i g where a reducti f re tha 24% i the ve ti ated r f is evide t 9 the ther ha d c sideri g the c paris betwee the ve ti ated a d the aid r f the differe ces are c siste t y reduced eve by re tha 50% The te peratures f the i trad s f the ti e were the sa e a d th se f the air i the ASV differed f r 4 D c rresp di g t 8 7% As regards the heat f ux the differe ce betwee the average va ues was f ess tha 4 WE 2 equa t 11 3% whi e e ergy required f r c i g was reduced by 9 8%  Figure 17. Average values (interval 12:00-15:00) for period one and period 2.
I Tab e 2 the ab ve described differe ces are r a i(ed a d fr these c paris s it appears that the air per eabi ity f the a t e acc u ts f r ab ut 50% f the e ha ce e t a ve ti ated r f ca bri g

Conclusions
The experi e ta research carried ut at the Te4 eHub :ab rat ry f the U iversity t Ferrara ai ed at i vestigati g re i detai the behavi ur f a ve ti ated r f a d assessi g the actua c tributi f the air per eabi ity f a disc ti u us a t e F r this reas i the fra e f a wider research tw specific tests were carried ut a d at first a ve ti ated r f was c pared t a c p ete y sea ed e the the sa e ve ti ated r f was c pared t a s ca ed aid r f i which the eaves a d ridge i es were c p ete y c sed but the ver aps betwee ti es were t sea ed t a w air e teri g a d eavi g The resu ts c fir ed that the air per eabi ity f a disc ti u us r f p ays a fu da e ta r e i the i pr ve e t f the perf r a ces f the r f by reduci g the te peratures u der the c addi g ayer a d theref re reduci g the i c i g heat f ux a d the e ergy de a d f r c i g